Fix XmlTypeCheck docs

Change-Id: Ia6a394a0dd4fc74c2c2435e48104df367a6b714a
Merge "Fix XmlTypeCheck docs"
Followup If21705c2, Shorten remaining urls to the whatwg HTML spec.

Finish up with the /specs/web-apps/current-work/multipage/ urls that
haven't been updated to /html/.

Change-Id: I4dbee0477eea440b0e8f113b1d393c6e0c739c4c