Remove ":backend: html5" from *.txt files, move option to Makefile
Regenerate about.html

about.txt in 2014-02-26T03:23:07Z!fraggle@gmail.com included a change
about including the copyright notice, but it did not get generated
into the HTML version of the document.
Information about the in-dev progress of the project and snapshot links.

While people have the best of intentions for reporting bugs, it is a
bit frustrating to hear that a bug was already fixed, but they're
unaware of it, being on the latest official release. Hopefully this
will make it a bit more obvious to how they could check the current
status beforehand.