Changes.md file

This is the beginnings of markdown for the CHANGES (Changelog file). All (most?) of the bugs are hyperlinked. There's some code-type cleanup needed where the changelog includes some code, and for some reason there is some bad formatting around OTRS Version 1 changelogs.

In case someone wants to run with this on the OTRS side, I thought I'd provide a (hopefully acceptable) starting block to finish up.