Big type_traits update:
Added make_signed, make_unsigned and is_complex.
Added docs for some previously undocumented traits: is_signed, is_unsigned and decay.html
Added synonyms for some traits that have changed name in the latest C++ std draft.
Re-organised docs, moved docs out of the main doc build for now (it takes too long).
This also fixes issues: http://svn.boost.org/trac/boost/ticket/492 and http://svn.boost.org/trac/boost/ticket/1008.