Convert to HTML5.

Skipping optional tags decreased the total size of output files by
1022 bytes.  Truth to be said, I have also removed some content,
but optional tags played sosme minor part I am sure...  On the
other hand optianl tags were offset by some additional semantical
tags.  Some new elements were introduced, and on top of that
"article" is four character longer than "div".
Make "source at" comment shorter.