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'

Since written books are quite different from empty books, the
visual clue that they are different items is really needed in-game.

I've added a "clasp" or "belt-with-buckle" like element to the
png from default_book, keeping them very similar but also
immediately recgnizably different.

I added the new texture to blockmen's license list since it's
obviously derivative of his work.

The PNG was run through a minimizer/optimizer to save space.

To make water a little clearer and feel purer
Also correct lava alpha values from 192 to 191

The fixing of low density decorations allows returning to
sidelen 16 for acacia trees and cacti, previously sidelen
80 was required for low density decorations to appear
Also use sidelen 16 instead of 8 for mgv6 papyrus

To avoid processing spikes where catch-up is non-essential
Disable in: Lavacooling, grass growing, grass removal
and all fire mod ABMs

Bring humidity points closer to reduce distortion of voronoi cells
Slightly reduce size of hot and frozen biomes
Improve location of glacier biomes
Remove unnecessary snow nodeboxes from tundra to improve FPS
Add missing dirt_with_snow to taiga

Update 'disable fire' documentation in conf.example

Closes #544

If puncher inventory is full, then drop boat

Add 'buildable_to = true' to flowers and waterlily