Use XML files directly
Right now, we use spec files generated by the gl-xml-spec project. These are .lua files that are generated from the .xml spec files. This made sense back when the Khronos files were an arbitrary text format. But now that they're relatively easily parsed XML, we should use that directly.
The goal with this is that absolutely nothing about the style/structure coding should change. This should be purely a load-time thing, with any fixup needed done at that stage.
This should probably also mean that any fixes to the XML spec files should be done in the loader. The overall goal is to be able to download new specs with a minimum of glLoadGen changes.