TODO: Escape hatches

[Noeda]

Let user to wrap their own GLuint/whatever in most managed OpenGL resources and also to let them get it out. I'd prefer if this can be done in a consistent way across all the types.

[Noeda]

In general, I'd like to play more nice with anyone wanting to use raw OpenGL with Caramia. This would be one piece.

[Noeda]

I've added OpenGLResource which allows to take the raw resource out but I don't think there is a generic way to put stuff back in.