ADDED:
+ tut_006 is going to put a texture on that cube. To that end I've hooked into the SOIL library and written a little wrapper around it to help match the Shader:: and ShaderProgram:: wrappers.

FIXED:
+ should no longer crash on shutdown because we're no longer double-freeing the shaders. Instead they're freed as soon as they're linked into a ShaderProgram (which turns out to be good practice anyway).