Use cairocffi instead of pycairo

[jishnu7]

Pycairo is deprecated and doesn't have virtualenv support, cairocffi is drop in replacement and being actively developed. Like we planned for pypdflib, we should use cairocffi here also.

[copyninja]

Can we have it part of Gsoc 14 milestone?

[jishnu7]

yes. But this is a simple task, I would like one of the students to pick it up as a pre-gsoc work.

[thegeorgeous]

@jishnu7, using cariocffi raises errors like this

TypeError: must be cairo.Context, not Context

This is known issue. Please refer the comments of cairocffi's author here:
Kozea/cairocffi#70

[copyninja]

@thegeorgeous You are free to propose a better way to use cairocffi I don't think we have very huge API's so shifting from pycairo to cairocffi should be fine.