Finish up framebuffer objects

[mikolalysenko]

There are lots of gaps in the framebuffer object API which we need to fill in. Also the constructor is currently untested and allocates a bunch of garbage. The following needs to happen before we release 1.0:

• We need complete test coverage for framebuffer objects and all code generation pathways associated to them
• There should be a method for quickly resizing or updating a framebuffer. Calling it repeatedly should have no effect.
• We need maybe 1-2 more good examples showing different uses of framebuffers

[Erkaman]

Once framebuffers are finished, I can implement some examples showing usages of framebuffers. I was thinking about implementing a simple blur post-process effect, shadow mapping, and maybe also a simple deferred renderer.

[Erkaman]

This is not finished yet though. We also need some examples.

[Erkaman]

I will work on that when I have the time.