add metafiles. These files contain information that is relevant for one

document but all variants of it (i.e. one basename), such as avail. languages,
formats etc.

(Note, that it's still a noop for the output.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@99330 13f79535-47bb-0310-9956-ffa450edef68