* The existing HTML documentation under doc/html-manual has been
converted to Markdown. This was done automatically using Pandoc, plus
some manual work to give identifiers to sections and changing internal
links to point to those sections with \ref.
* The Doxygen front page now contains some content: a link to the
doxygen-ated HTML manual, and a note about the API documentation. The
intention here is that the entire Doxygen site could be hosted
publicly, serving both users of and contributors to CBMC from a single
site.
* The doxyfile is updated to enable these changes.