Update documentation

OK. This is mainly the old pull request, but without the controversal changes.

I've retained and updated almost all external links.

69e2eca (Matthias Maier, 6 minutes ago)
   put license.html directly on the homepage

291da67 (Matthias Maier, 18 minutes ago)
   clenaup toc, remove stale information

0ee8723 (Matthias Maier, 5 months ago)
   Documentation: remove stale html files

   Remove news.html and publications/indexl.html stubs - they are not
   referenced any more.

716aba8 (Matthias Maier, 5 months ago)
   Documentation: Remove all references to external resources

   We already link to this  external resources on the homepage - there is no
   point in doing it here (nobody will find it and it has the bad tendency of
   being out of date).

2b7387b (Matthias Maier, 5 months ago)
   Documentation: Remove svn.html from offline documentation

   The new development guidelines for git should be prominently on the
   homepage, not buried in the offlinedocumentaiton. So just remove the old
   cruft.

1af900e (Matthias Maier, 5 months ago)
   Documentation: Remove bogus indentation.html file

   Well, we already have a detailed doxygen file about indentation. So it is
   better to add the three relevant lines about astyle there and remove this
   additional documentation page completely

64e1c28 (Matthias Maier, 5 months ago)
   Documentation: Remove references to svn

   Remove references to svn's $Id$ in the headers and replace references to
   the old subversion repository in various html files

e89b226 (Matthias Maier, 34 minutes ago)
   Fix link in step-52