Bookmarklet does not filter out unrecognized attribute errors

[mattfellion]

This issue is related to #5.

Disregarding the special case of "ng-" attributes, in general the bookmarklet does not filter out unrecognized attribute errors. (These are errors of the form "Attribute x not allowed on element y at this point".)

My sense is that these errors shouldn't remain in the results. For reference, WCAG 2.0 Parsing Criterion is a PITA (2015) says unrecognized attributes are not WCAG parsing failures, and they are not listed in WCAG 2.1 parsing error bookmarklet (2019).