Subversion book and translations moved.

The Subversion book sources (in doc/book/book and thereabouts) and its
translations (de, nb, es, ru) have been moved out of the Subversion
source code repository, and into a repository at:

   http://svn.red-bean.com/svnbook/

where they can live more closely integrated with the Subversion book
website (at http://www.svnbook.com/), and provide translators a home
for their translation projects.