Add a glossary for the apache docs. This is NOT based on the Covalent glossary

Add a glossary for the apache docs.  This is NOT based on the Covalent glossary
because we couldn't work out the copyright issues.  Instead, it is based on
Ralf's work on the SSL glossary plus my own additions.

More entries are very welcome.  I tried to make this an "index" of the docs as
well as a glossary -- I included links to other places in the docs with more
information wherever possible.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96138 13f79535-47bb-0310-9956-ffa450edef68