Drop support for CFFI < 0.6
Gradients (still untested), handle pathological cases.
Add radial gradients.
Flake8.
Remove the scripts for runnig the W3C test suite.

Moved to https://github.com/Kozea/WeasySuite
Fix a bug introduced by "whitespace only" changes :)
Add parsing tests for gradients.
Fix a test broken by 1d1bf9cd
Fix 'white-space: nowrap' and add tests about this