Continue new platform/glium implementations

- Assets, asset manager system
- Rendering system trait
- Kick off glium platform implementation
- And more

raidillon_glium/src/lib.rs

@@ -2,6 +2,9 @@ pub mod platform;
 pub mod assets;
 pub mod model;
 pub mod gltf_loader;
+pub mod system;
+mod render;
 
 pub use assets::GliumAssetManager;
 pub use platform::GliumPlatform;
+pub use system::RenderingSystem;