Merging part of Oct 26, 2019 upstream commit

Reworking of XML end tag handling.

This does break my fork.

Clean up credits

De-emphasize end tag

My preference is for the end tag to be less visible. This makes that
happen.

Half of the time, my XML files are actually XHTML, and I am closing
blocks with...

</div> <!-- class name -->

Highlighting these lines with differing colors is distracting, and it
would be too difficult to find a way to pattern match these types of
comments. Therefore my preference is to not highlight at all.

Updates

I don't know the history of these changes, but this is how I found the
XML vim syntax file when I began my fork.

Initial commit following rebuild