Document ale pseudo-functions.

Change-Id: I4a0e1a145f179315277b611dca6144711553f8e9
Reviewed-on: http://review.couchbase.org/37526
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>