Wrap textures in Texture objects.

This will help if we ever want to port to Direct3D and also improves safety
because it ensures textures are cleaned up properly.
Merge pull request #15 from pcwalton/texture-wrapper

Wrap textures in Texture objects.
Remove the now-unneeded TextureManager.
Merge pull request #16 from pcwalton/no-texture-manager

Remove the now-unneeded TextureManager.
Remove the now-unused ImageLayers and fix a bunch of warnings
Add a flag to flip layers for GPU rendering.
Merge pull request #17 from pcwalton/flip

Remove ImageLayers, fix warnings, and add a flag to flip layers
Merge remote branch 'origin/master-upgrade' into HEAD

Conflicts:
	layers.rs
Put textures in an ARC so that they can be reused
Merge pull request #18 from pcwalton/texture-arc

Put textures in an ARC so that they can be reused
Merge branch 'remove-glut' into master-remove-glut
Merge branch 'remove-glut' into master-remove-glut

Conflicts:
	rendergl.rs
Merge pull request #20 from metajack/master-remove-glut

Remove glut on master
Merge pull request #27 from kmcallister/rust-upgrade

Update to latest Rust
Switch from -o to --out-dir.
Merge branch 'master-upgrade'

Reverts commits that weren't present. Those are now on cpu-rendering branch.
Specify which end of the list when adding child layers
Merge pull request #28 from eschweic/layer-order

Specify which end of the list when adding child layers
Factor out the texture rendering and delete unnecessary layer types.
Add flipping and modernize the codebase a bit