Swap from XHTML to straight html5

Also fixed validation errors, the other files may need to be edited as
well.
Additional fixes to HTML validation

Fixed the entire site (as much as I have with this local copy  so I can
sync with the upstream) validated every page with
http://validator.w3.org
Full fix to HTML validation and formatting

So, this is the final edit for now. All files now validate properly.
The formatting of the lecture pages nearly identically matches the
original, mostly margins (and if it isn't perfect, I kept it because I
felt it looked slightly better)
Additionally I pulled from the upstream, so I have every page that is
currently on the site.
Merge pull request #32 from LinkSlayer64/master

Swap from XHTML to straight html5