* Move LaTeX docs into a tex/ subdirectory of the doc/ dir

* Add a Makefile in doc/tex/ for generating PDF and HTML
* Add a README.txt file to doc/tex/ to document which tools are used and what
  web sites to visit for getting them.
* Update build_tools/prep_tarball to put the proper Asterisk version string
  in the automatically generated PDF for release tarballs


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@72982 65c4cc65-6c06-0410-ace0-fbb531ad65f3