Add a new DTD for a basic page in the users manual, and take out the common elements from

this and modulesynopsis.dtd into a common.dtd file.

Submitted by: Astrid Kessler <kess@kess-net.de>, Joshua Slive


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@96062 13f79535-47bb-0310-9956-ffa450edef68