Document all meetme realtime fields, and in the process, make some field lengths more consistent.

(closes issue #15493)
 Reported by: lasko
 Patches: 
       meetme.diff uploaded by lasko (license 833)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@206567 65c4cc65-6c06-0410-ace0-fbb531ad65f3