Add memory-related stats to the memory-stat cmd

Change-Id: I95e419d6dc3429a63fa7f50fa5b744a7b2d7f34e
Reviewed-on: http://review.couchbase.org/38319
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>