sphinx: cheesy script to convert .tmpl files

This script uses pandoc to convert existing DocBook template files to RST
templates.  A couple of sed scripts are need to massage things both before
and after the conversion, but the result is then usable with no hand
editing.

[Jani: Change usage to tmplcvt <in> <out>. Fix escaping for docproc
directives. Add support the new kernel-doc extension.]

Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>