Merge tag '0.0.3' into develop

Release 0.0.3.
Refactored level building outside of Level
Faster patch loading & blitting.

Cuts loading times by about 10x in unoptimised mode and by 6x in release mode.
Some cleanup of image blitting & loading
Non-square wall atlases.

Support recatngular wall atlases. Generation is also changed to a random
shuffling and transposing to attempt to stuff the textures into an atlas as
small as possible.
More consistent shaders.
Brightness issue fixed.
wall_atlas -> picture_atlas since it's general
Removed level double loading.
Refactored main a bit. Bumped version to 0.0.4.
Merge branch 'release/0.0.4'

Behind the scenes minor release. Change log:
* Optimized level loading for 6-10x speed up.
* Smaller atlases (non-square support).
* Refactored and simplified shaders.
* Refactored level building to a more generic system.
Merge branch 'master' of github.com:cristicbz/rust-doom