gl-0.4: TODO.markdown

Things that would be nice to have
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* Add a class for things that can be converted to `GLenum`'s and use it instead of `GLenum` in negative position in the bindings?
* Some of the manual pages are for multiple functions, link by prefix?
* Fix issues on Windows caused by the large number of modules
* Fix distribution issues caused by having a custom `Setup.hs` with non-trivial content.