Add runtime access to CAIRO_HAS_* constants in cairo-features.h
Submitted by James Tocknell
Assigned to Chris Wilson @ickle
Description
Currently it is not possible to check for supported features at runtime. This would allow projects such as cairocffi (https://github.com/SimonSapin/cairocffi) to provide this information (see https://github.com/SimonSapin/cairocffi/issues/33). This would allow for such things as matplotlib using cairocffi instead of pycairo (which currently works HAS_* is added to the file).