fixed; populated streams

closes #1411
Add Aggregate implementation

closes #1400
refactor aggregation
aggregation; combine project + select

adds select syntax to project and removes select
tests; confirm aggregate().exec returns promise
Merge commit '3.6.3'
Merge branch '3.6.x'
Merge branch '3.6.x'
model.remove method callback is passed the removed model
test; added for 1419
test; ocd
Merge branch '1419'
refactor objectid
refactor; deepEqual
Merge branch '3.6.x'
Merge branch '3.6.x'
fixed; setting nested objects with null prop

closes #1326
examples; connection sharing

http://stackoverflow.com/questions/15957821/how-to-make-mongoose-connection-available-globally
examples; add readme
fixed; setting nested mixed paths

closes #1418