Improved lighting model; using same calculations for flats and walls with light level scalar adjustment.
Set LIGHT_SCALE to 2.0.
Defined DIST_SCALE and set it to 1.0.
Merge pull request #7 from JamesDunne/lighting-model

Improved lighting model
Reverted to GLSL 330 on non-linux OS-s.

This is a quick fix, it isn't really the way we should do this. The commit adds
the ShaderLoader struct which deals with loading shaders from files and
prepends the version directive based on the platform.

In future, ShaderLoader should be the one dealing with preprocessing shader
files in general (#include, #ifdef etc.)
Move BoundsLookup to tex.rs.
Small atlas building fix.

Before there was a problem if the same animation appeared twice in one level
using different frames; this would cause the animation to be added to the atlas
twice.

In addition to fixing this problem, this change also unifies the name->frames
conversion from the two atlas building methods into one external funciton.
A few cosmetic changes.
Merge branch 'feature/better-atlas-build' into develop

Conflicts:
	src/level.rs
Refactored everything into individual libs.