At the moment just the GL library itself w/o the tests, and without
backwards compatibility aliases. The following types were left in the
root namespace, despite being in the GL/ directory, as they will get
moved back soon:
* Image, CompressedImage and their dimensional typedefs
* ImageView, CompressedImageView and their dimensional typedefs
* PixelStorage
Not PixelFormat etc., that one will stay in the GL namespace and a
completely new PixelFormat enum will be provided in the root namespace.
The `#line` statement was an ugly hack and it breaks code highlighting
in KDevelop (and I guess in many other Clang-based IDEs as well). This
however means adding new extensions is a bit more annoying, but
hopefully the newly added test should aid with that. Developers guide
contains more info.