Add bindings for some of COGL constants
Add bindings for some of COGL constants

COGL exposes some of the GL constants as CGL_ macros, so that the same
symbol is available on both GL and GLES.

This commit installs the same symbols under the clutter.cogl module,
at least for the same macros Clutter and COGL use internally, or
document in the API reference. Adding all the symbols would be pretty
much useless: a lot of them are usable only if you drop to GL anyway,
and for that we have PyOpenGL, which already exposes those macros.

pmarti/pyclutter,pmarti/pyclutter,GNOME/pyclutter,pmarti/pyclutter,GNOME/pyclutter,pmarti/pyclutter