Merge pull request #1 from mfairchild365/master

Implement pa11y
Merge pull request #3 from mfairchild365/config

Allow ignoring rules
Change to a graded by default

instead of pass/fail.  This is because accessibility machine testing is objective, and does not accurately  reflect whether a page is accessible, or inaccessible.  Also, it is possible for a page to be mostly accessible, with only a few errors which could hinder accessibility.
Merge remote-tracking branch 'upstream/master' into config