working on draft API
working on initial pipeline stages
implement test for aggregation of states of 10M as show here http://docs.mongodb.org/manual/tutorial/aggregation-zip-code-data-set/#return-states-with-populations-above-10-million
add test/example for average city size
add support for documents as _id for group()
add support to enable the "Largest and Smallest Cities by State" example from the docs
tweak method names
expose ReadPreference and AggregationOptions as parameters
$out support and test
test $limit and $skip
add support and test for $unwind
add support and test for $unwind
fix $unwind test.  all working now.
beginning $geoNear support
link back to example docs
reuse Query classes for $match
use the existing Query API for aggregation query clauses
save the query in a local variable
rebasing with master
rebasing with master
finished rebasing with master