Apply various cosmetic changes to README file
Merge pull request #379 from weiss/polish-readme

Polish the README file a bit
Fix upgrade of PubSub mnesia tables from older ejabberd version.
Give temporary processes time to stop cleanly

Allow temporary processes to perform some final actions when shutting
down.  For example, moc_muc_room:terminate/3 fails to send 'unavailable'
presence to the room participants when killed immediately.