Create OpenGLFrame for darwin / OS X

[einarf]

Should be more than doable to make an OpenGLFrame for darwin.

It's needs to properly separate 2.1 and core contexts because OS X only supports 2.1 or 3.3-4.1. There is no backwards compatibility once you go 3.3+ (pure core context).

The context needs to be flagged with core and forward-compatible for 3.3+.
In all other instances a 2.1 context will be created.

I will probably be looking at this in the near future unless someone else grabs it.

[einarf]

Got a context created in OS X, but there are still some issues with the framebuffer to resolve. This is the demo.py example with no output to the window framebuffer..

[einarf]

More information in the pull request : #11