Too tired to do some code, prepared documentation:

- Makefile.am configure.in doc/Makefile.am: added a doc subdir
  and the rules to generates the makefiles.
- doc/libxslt.sgml doc/xslt.html: very first version of the manual
- doc/html/*.html : autogenerated documentation
- libxslt/xsltInternals.h: fixed a typedef wich was breaking gtk-doc
Daniel