CanvasRenderingContext2d#filter

Like patternQuality, but applies to transformations effecting more than just
patternsi (i.e. the implicitly created pattern).

See
http://cairographics.org/manual/cairo-cairo-pattern-t.html#cairo-pattern-set-filter
for more information.
Merge pull request #278 from mojodna/filter

CanvasRenderingContext2d#filter