This merges the current state of the well-maintained and tested
`torches` mod as I've maintained it for the last 6 months.

This started out as a thorough cleanup of 3D torches by blockmen,
where some of the initial code still remains.

The models were redone entirely from scratch and have been extensively
tested with dozens of animated textures converted with mcimport,
and look a lot better than the original 3D Torches mod.

The ceiling torch is retained and functional. The `wieldlight`
addition that the torches mod has was removed, since it relies
on wieldview to look decent. This can stay external mod code.

I've opted to move the torch nodes to a separate file. It's not
a lot of code but nodes.lua is already huge, and I wanted to
retain the copyright header and some of the readme.txt notes,
and this was the easiest way of doing it.

This code passes "default:torch" to nodes with on_rightclick,
fixing problems with itemframes. Essentially it has a more
elaborate item_place() routine to make sure we're not passing
the wall torch to nodes that may display it.

The ceiling torch is a separate model and not the same as the
floor model. That does mean that there are 3 models in this
mod.

Stereo sounds are not played positionally, which should never
happen. Convert this track to mono to fix.

This makes the itemstrings consistent over the whole file.

Plus one silent sound to break repetition 'default_water_footstep.4.ogg'.

This is all the working code from SmallJoker's boost_cart, poored into
a more suitable form for minetest_game.

- Mesecons and moreores stuff was removed entirely.
- Textures were all renamed and moved out of default/
- Updated license, readme.txt, attribution
- Changed code license to MIT, left artwork at CC0
- removed default:rail and made aliases for it
- :carts:rail is now carts:rail.
- localized entity def
- removed copper rail entirely
- startstop rail was removed, as well as detector rail
- remodeled to b3d using stujones11 excellent blend model, but sizes
  of cart adjusted to make pixel sizes consistent (0.625) everywhere.
- slightly more complex texture map for the cart (front/side visibly
  different)
- rail parameters are passed as a separate def table, and stored in
  a private list. This avoids having to call `get_meta` on every
  node. In return, we need the node name, though.
- adds metal sounds (based on default metal sound function) and
  cart moving sound.
- reduced cart speeds to max 7, 5 by pushing.
- Added on_step() rail event handler, gets called when a cart is on
  a rail.
- Added various rebased updates from upstream (thanks Krock)
- Included a fix that removes the 'reverse jiggle' when stopping.
- Included reworked textures by sofar.

The mod namespace is still public, but I'm NOT declaring it an API. I'd
rather see it localized instead, for now. Any public interface in this
code is *experimental* at best, and should be considered non-stable and
unsupported for now.

Currently all minetest_game PR's are failing travis since the
upstream luacheck now also warns about whitespace issues, and
there are a few of those in the code. This fixes all of them
so we can yet again rely on luacheck.

With mip-mapping enabled, some GPUs cause a visual bug with indexed
textures that use alpha. This bug has been present for a while but
not noticed before. All indexed alpha textures must now be converted
to RGBA, to start this process we revert some textures converted to
indexed in the recent commit af3c9186.

When placing boats, align the boat with the player's yaw.

Align drivers yaw with boat yaw when entering a boat, would previously turn
boat yaw by player's yaw + 90° to the right.

Make lava cooling ABM use a new group 'group:cools_lava'.
Nodes other than water can cool lava. We assume snowblock and ice melt,
turn to water and cool lava.
Leave 'group:water' present temporarily to not break mod liquids.

These will automatically play when a tool breaks.

This fixes the missing item issue in creative inventory caused by using
1 instead of 0 for 'start_i'.

This fixes all cases where the color profile was broken, and
libpng warns about. It also makes almost all textures indexed
instead of RGB where possible (textures that don't have
semi-transparent pixels).

To be consistent with the snow slab.

Rename slot icons.

Add on_ignite functions to tnt, gunpowder, coalblock.

A deeper, darker level of leaves is created by tiling the texture
2 by 2, reducing brightness and offsetting this.
For a denser leaf appearence with the 'simple leaves' setting.
Also used for acacia bush leaves.

Selection box width is limited to 14 / 16 node to visually
distinguish box from any neighbouring cubic nodes.

Edited fuels: fences, wooden ladder.
New fuels:
boat, paper, book, dry shrub, stick, vessels shelf, wooden tools,
wooden door, trapdoor, fence gates, farming crops, stairs, slabs, beds.

Some code simplifications.

The purpose of this is to allow mods to be able to interact (e.g. fill up)
an empty bucket when it is used to punch a node that's not a liquid source
or when punching a custom entity (e.g. milking a cow).

- Use opaque texture for top+bottom of iron bar
- Add color variation for iron bar top/bottom
- Add paramat's texture to credits
- Update license info for paramat's textures

This plays when damage is disabled, an engine bug.
We can remove it because both sounds are identical, now it is removed
the 'player damage' sound still plays when falling damage is taken.

To allow mapgen bushes in green-grass and savanna grasslands.
Nodes for a generic bush and an acacia bush.
Stem nodes are craftable to a single wood node to provide a small
amount of wood resource in grasslands.
Fuel times are that of corresponding 'wood' nodes, 1/4 that of
corresponding tree nodes.
No leafdecay to enable use as hedges or without a nearby tree trunk.
Uses 'default leaves simple' texture for extra visual thickness.

Use 'player damage' sound for both damage and falling damage.
Gains for damage sounds are set in the engine, however we cannot change
those gains as other subgames already use damage sounds based on those
gains.
Sound has been re-edited from source and normalised to 0 dB for
maximum volume, which is only just enough because gain is fixed at 0.5
in the engine.