Fixed texture and buffer constructor and destructor declarations.
Only delete the VAO if it exists.
Added a method to get the internal format of a texture level.
Add a framebuffer object.
Fixed a warning about casts.
Renamed some glGet* functions.
Integrated framebuffers into the GL state.
Implemented desktop gl framebuffers.
Implemented glReadPixels.
Implemented glFlush.
Implemented glFinish.