elements inside headings) and also use a lower heading, h3 and not h1
for the subheadings.
Reduce the amount of code duplication with include's for each VCS.
return a list with selectors as keys, otherwise the main menu won't
link the active revision, but instead use the main branch
* changelog.html, tree.html: shorten the branch / tag output a bit
(still ugly to have a fixed output like this, though), link tags
by their selector, no longer by their revision ID. We loose some
flexibility here, since tags could actually mark different
revisions, which are now ignored