Recommend mod screenshot size in lua_api.txt
Adjust displayed screenshot size of texture packs
Document texture pack files in lua_api.txt

@kilbith spotted correctly that I had accidentally removed the
"soft" edging on the minimap overlay by converting it from RGBA
to Indexed, which killed the transparent pixels on the edging.

Related: #3730

This adds a simple, and small "North" indicator to the circular
minimap. The indicator is in a classical triangle-like arrow with a
little bit of shading to accentuate the shape and give it a little
bit depth. The indicator is stuck exactly at the edge as far outwards
as possible, and is not too intrusive but still easy enough to spot.

Having a non-power-of-two image broke the Android app.

Used PNGOUT, OptiPNG and DeflOpt.
Removes ~350 KB without any loss in quality.

There have been plenty of ppl involved in creating this version.
I don't wanna mention names as I'm sure I'd forget someone so I
just tell where help has been done:
- The partial android versions done by various ppl
- Testing on different android devices
- reviewing code (especially the in core changes)
- testing controls
- reviewing texts

A big thank you to everyone helping this to be completed!

Also add a menuheader, menusplash, menufooter_clouds, and allow HD menu footers.
And finally don't git-ignore textures/base/.