Tonnes of stufferinos!

Lights: Added simple struct and method for getting the transform for
shadow mapping.
Added shadow mapping for spotlights.

RenderingEngine: Added post-processing!
Compacted shader loading with new constructor.
Now has a set of shadow maps that are shared by all lights, resolutions
are powers of 2 (up to 1024).
Constructor also sets a bunch of textures that are used as render
targets for post-processing.
Actually unloads things in the destructor now.
Currently passes FXAA and Bloom onto the display texture.

***A bunch of new shaders have been added!

Shader: Added constructor for single-line loading.

Texture/TextureData: Now supports mipmapping and anisotropic filtering!