Removed obsolete documentation.
Removed most customizations from generated docs.

They had become unmaintainable with recent versions of Doxygen, and were
missing the new features that were added.

The offline and online versions were merged, too, with the glitch that
search doesn't work in the offline version (which, however, I'm not even
sure I want to keep distributing...)
Logo now links to home page.
Unify user and developer menu.

The unified menu is divided in sections for better navigation.
Style index.shtml as splash page.

The user menu is not front and center, with the mission statement below.
A similar change was made in the 404 and 410 pages.
Shortened mission statement.

The information at the end was already available in the links above.
Add style overrides for small screens.
Updated style for printing.
Used same font for subtitle in reference docs.
Logo now links to home page.
Reorganized web site menus.
Merge remote-tracking branch: upstream/master