Update QueueMemberStatus event documentation to include member status values

Update QueueMemberStatus event documentation to include member status values

The Status: header in a QueueMemberStatus event (and other QueueMember* events)
is the numeric value of the device state corresponding to that Queue Member.
As those values are not exactly obvious, listing them in the documentation is
useful.

Matt Riddell reported this indirectly through the wiki page.

(closes issue ASTERISK-20243)
Reported by: Matt Riddell
........

Merged revisions 372531 from http://svn.asterisk.org/svn/asterisk/branches/11

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@372538 65c4cc65-6c06-0410-ace0-fbb531ad65f3