Implement a rudimentary pull with nested arrays.
Add support for $pull with positional operator.
Missing pymongo import in tests for pymongo.errors.ConnectionFailure usage.
Add $push functionality.
Add positional operator for $inc. Also, fix an issue with multiple edits and positional operators.

The problem was that the document would change after the first edit command.
This would result in the spec not matching on the second edit command and
thus the second edit not succeeding.

So we now store the subdocument in the update method. If the subdocument is
found, we can simply reuse it.
There are cases in which the document can contain an array. Mongo handles it and so should the mock framework.
Remove dangerous stub for $where
Fix find_and_modify behavior with remove, new (#49)

* No longer accept remove and new, remove and update
* Propery support remove
Fix README
Fix $push and $pull to handle more cases.
Add more tests cases to test suite for $push, $pull, and $inc.
Fix resolve_key_value to check for specific list items.
Merge remote-tracking branch 'upstream/master' into pull-nested-arrays
Fix issue where we need to use iterkeys from six.
Revert imports to what they were before.
Merge pull request #48 from Evgenus/master

as_class parameter added to find
Merge pull request #51 from abc2mit/fix-search-in-array

Fix resolve_key_value to check for specific list items.
Acknowledgements
Fix deepcopy issue with classes deriving from dicts (#52)
Fix exception handling in test