Node timers are higher precision and a better guarantee
of happening at regular intervals, whereas ABM's may be
postponed, cancelled or missed if a player is too far.

The largest benefit is that once the furnace is done
cooking, no more ABM's are fired - the timer is stopped
instead and no more events are created until items
are put in the furnace.

This patch is larger due to the migration of the timer
function and indentation change as a result of the somewhat
reduced complexity. I've tested with several furnaces and
this works correctly and behavior is not affected, although
people may find that their furnaces now work more
regularly.

If you place several furnaces next to eachother, you will
still find all furnace timers firing exactly at the same
time. This is a bug in core that should not coalesce node
timers at second intervals.

This patch replaces the default door nodes with a new mesh model
and nodes.

Two new models were added that are 2 blocks high. One for left-hinge
and one for right-hinge doors. This allows us to make a single texture
fit on both models. The alternative would have been 1 model and 2
unmapped textures, which is more work for mod developers.

Doors work exactly like the old doors, including ownership, breaking
doors, opening and closing.

Under the hood, we can prevent the top part of the door from being
obstructed by placing an invisible node. This prevents liquids from
flowing through doors or people placing sand or other blocks in the
top half. The door code automatically places and removes these as
needed.

Metadata is used to store door state, just like the old version.

A doors API is added, it allows mods to use the API to open/close or
toggle door states without worrying about sounds, permissions and
other details. This is intended for e.g. mesecons. This API allows
mods to manipulate or inspect doors for players or for themselves.

In-game old door nodes are automatically converted using an ABM and
preserve ownership and orientation and state.

TNT blows up all doors and trapdoors except for the steel ones,
who can survive a blast. We return an itemstack in on_blast(),
which requires a TNT API patch which is also pending.

We enable backface culling for most of these doors, as this gives
the identical visual appearance that the old doors had. In the case
of the glass door, there's a slight twist.

The texture files used by the new doors have new names that do
not conflict with previous texture file names to avoid texture
pack conflicts.

Thanks to red-001 <red-001@users.noreply.github.com> for some
of the conversion code, cleanups, and extra textures.

Avoids trees or large cacti being placed multiple times at a single
position, by changing the node at the heightmap y value

This converts the call to minetest.register() for the default
fence node, so it can be called by other mods to quickly
setup other fences.

Since this creates an API, insert it into the game_api.txt.

The api looks like minetest.register(name, {def}), and has two
uncommon fields: "texture" and "material". Any normal nodedef
property can be passed through, except "drawtype". The "fence"
group will always be added.

The default fence recipe is modified to be as follows:
  wood, stick, wood
  wood, stick, wood

This recipe yields 4 fence nodes.

This allows us to create according recipes for acacia, pine,
aspen, and junglewood fences without adding new stick types:

  pine wood, stick, pine wood
  pine wood, stick, pine wood

This is a from-scratch implementation, written by heart but inspired
by (#665 - Add many wooden fences).

Stick and fences nodes are named in a consistent way.

as above, the avility to dye coloured wool whilte again.

We may want to use biomes here at a later stage.

Organizing these in groups will allow mods to do several things
easier:

- create craft recipes using them as ingredients
- manipulate map nodes based on group properties

There are quite a few slab and stair blocks already, so automatically
add these groups at registration time for all of those. Since most
mods I've seen use the registration code in this submod, they will
also benefit.

We're using a normal wooden side texture to draw the sides
of trapdoors. But the side textures have only 2 edges that
have a nice texture for the 2px wide trapdoor. We can
either repaint the textures, or just rotate the texture
properly for the two sides that need it.

Because the side texture for wooden doors was just a default:wood
texture, it clashes with the colors in the trapdoor, and so
we add a wooden trapdoor-matching tile side texture as well.

This also improves the steel trapdoor side, but without a
texture change there since that was already a specially
drawn texture for that node.

We also increase the thickness of the trapdoor to 2px. Right
now the model is 0.4 large, but this causes the side textures
to look odd as there's a mismatch in pixel size. By scaling the
trapdoor side up to exactly 2px, the sides look natural.

Thanks to @kilbith for the suggestion.

There really is no reason to prevent rotation in trapdoors, I
expect this to be an oversight.

Trapdoors work perfectly well sideways, upside down and can
work like fences, gates and more. Most commonly, people will
want to put them in the top half of the node so they remain
flush with a floor.

Adds a birch-like tree to the default_game. Aspen was chosen on
purpose instead of birch, as several birch tree mods already exist
and choosing a different name avoids any conflicts.

Schematics were made for both normal and sapling version, assuring
saplings will not be able to grief. The shape of the Aspen is "fanning
out at the top" and provides an easy tree to walk under, but still a
somewhat thick cover. The Aspen trunk is 4 to 6 blocks tall, with up
to three layers of leaves on top, making it slightly taller than an
Apple tree, but shorter than a Pine tree, which provides a good blend.

Textures were painted from scratch, except tree_top and _wood
variants, which are color modified versions of the pine_wood
variants. Appropriate licenses have been chosen for the new textures.

The leaf texture is light enough to contrast other trees, but dark
enough to offset against our light default grass color. The leaves
are drawn in the typical minetest default fashion with plenty of
transparancy, but enough definition to suggest that you're seeing
something that looks like leaves. The placement of leaves in the
schematic also suggests the top of the tree is sparse and you can
see the sky through the leaves.

Sapling texture is both traditional and different, with lush green
leaves and a well-defined stem, but slightly stick-like and skinny,
as these plants tend to grow up first, then out.

Add fallen Aspen logs. We make these logs a minimum of 2 blocks long,
and up to 3. This allows us to make these logs a place where both
red and brown mushrooms can be found, to these may be attractive to
players. However, the spawn rate for these has been reduced a lot
compared to the other logs, to account for the scarcity of Aspen.

Add stairs, slabs for these wood types as well.

Mapgen will place these trees in deciduous forests only, but in
a way that the biome is a range between entirely Apple trees, and
mostly entirely Aspen trees, with a bias to Apple trees. To make
fallen logs somewhat correlated with trees, we modify the planting
of Apple trees and logs to use perlin noise and not fill ratio,
otherwise you'd always end up with Apple logs in Aspen tree areas,
which would be suspicious. There still is a bit of a mix.

In oversight, I added this recipe not verifying that it was already
taken.

We change this to a 2x2 iron bar recipe. The shape and amount are
reasonable (reduced to output 1 steel trapdoor), and I verified that
it wasn't in use.

Fixes #779

These were likely too high, so we lower them to the rate
of mushrooms on apple trees.

issue #773

This is a non-issue: these are aliased to normal mushrooms. For
clarity, we replace them with the normal mushrooms here as well.

We can vary the landscape a bit more by placing "fallen logs"
around the various forests. These decorations are quite fast
and will provide some gameplay value but are still more rare
than the corresponding trees, so they don't provide free
materials.

I've manually put the schematic as lua tables since these log
schematics are only 8 blocks. We vary the log lengths between
1 and 3 blocks by making the end blocks have a lower chance
of appearing.

Amount is varied by fill_ratio, except for acacia trees where
we reduce the scale, so that acacia logs show up near places with
acacia trees consistently.

Mushrooms are placed optionally on each log. We can't place
two different mushrooms on a log, so instead we opt to place
brown mushrooms on oak/appletree logs, brown mushrooms on
jungletree logs, and red mushrooms on pine logs. No mushrooms
are placed on acacia logs, as they occur in a dry biome,
savannah, and this adds a bit of biome diversity.

Closes #770 - thanks to @tenplus1, @kilbith

Combine any written book with an empty book to copy it. The
copy is in player hands when using, and the original is put
back on the crafting grid and can be directly copied again.

All ownership and metadata is retained, so the copy of the book
is as writable as the original is, or isn't.

Adds a steel trapdoor. Textures were painted from scratch, and
inspired by the current Steel Door. Ownership on the trapdoor
works as expected, and so does the crafting recipe.

Playing stereo sounds positionally in OpenAL causes it to play
the sounds unattenuated - same volume for all distances. This
shouldn't happen, and makes door sounds unneccesarily loud from
very far away.

Convert all door samples to mono, 22kHz 64kbit.

Trimmed all door samples to remove lead, trail silence.

These have almost no value gameplay wise. Mushrooms spread
by their very nature into appropriate soil nearby, and
harvesting spores is something only scientists do. Actual
mushroom farmers leave a few mushrooms and put on more
manure, and keep the light off.

Modify the growth ABM to test for light levels and attempt
to plant a similar mushroom nearby (+/- 2 x,z, +/- y). Light
at both source and destination needs to be low enough. I've
tuned it to be 3-4 spaces from a torch.

Mushrooms will die in full sunlight, but they can survive under
trees and may grow out at night anywhere.

Removed obsolete textures.

Remove unused nodes and provide aliases for them.

Aliased obsolete nodes so no unknown item nodes appear.

Mushrooms die only in full sunlight (light level 15).

This prevents nodes that are not of the "facedir" paramtype2,
as these are generally not expected to be able to rotate. Mods
and other methods may still manipulate param2 of these nodes
as expected.

Addresses #712

Re-align parameter format in 'register ore'