add custom repeat-x/y processing

[calvinsomething]

Fixes createPattern repetitions "repeat-x" and "repeat-y" behaving as "repeat."

It seems only fill is necessary to change, as with HTML5 canvas using stroke with either x or y options behaves the same as repeat.

Here's the visual test:

• Have you updated CHANGELOG.md?

closes #2049

[zbjornson]

Looks good, just one little thing.

[zbjornson]

Thanks! Landed as c6a1546 -- I ran yarn lint --fix and updated the changelog but didn't want to push to your branch without asking.