Stubs for ImageTexture
Merge branch 'master' into image-based-textures

Conflicts:
	Makefile
Fix missing `std::` prefix
Use ImageTexture in test scene
Read image from path at construction of ImageTexture
Add fallback "missing texture" color
Add rock texture image
Add TODO
Merge pull request #23 from merlinND/image-based-textures

Image based textures