Unsupported cairo features

[SimonSapin]

cairo still has a bunch of features that cairocffi could expose, but doesn’t yet. utils/cairo_coverage.py lists cairo functions that are not used in cairocffi, which is a pretty good indicator of such feature.

Feel free to comment of missing features you would like to see added.

[stuaxo]

Mostly cairogl :) working out how to build my own deb with it enabled at the mo..