Haskell OpenVG binding

Copperbox revision 401.

Finished haddocking the exposed modules in the OpenVG binding. There are a few functions that I haven't translated yet (e.g. vgGetMatrix), and I'm not sure if some of functions are missing on in the ShivaVG dll on Windows due to my compilation hack, but most of the code is done.

The VGU module remains a bit of a sore thumb - although it makes some functionality more high-level, it does it is a way that is particularly un-Haskell. It might make most sense simply to leave it as is, and define a original higher-level interface.