New xsl file which generates ready to copy/paste strings for prettify(.min).js

All the directives are collected in some JS arrays, so that it is easier to upgrade the list
in prettify.js when new directives are added.

'build.sh' will be updated accordingly. A new build target ('prettify') will be added to
update this list. The resulting file is: docs/manual/list_for_prettify.txt

This new file is heavily inspired from convmap.xsl.

It should be possible to go further, but this is already a first step.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1828598 13f79535-47bb-0310-9956-ffa450edef68