Add `refractionIndex` field to `Ray`
Refraction test scene
Ideal transmission
Add current render example
Add specular transmission exponent property to materials
Add specular transmission term (light through glass)
Add some explicit dependencies
Merge branch 'master' into renderer

Conflicts:
	Makefile
	src/main.cpp
Merge pull request #18 from merlinND/renderer

Specular lighting (glass)