Merge pull request #29 from jamplify/master

Handles excludes on discriminated Schemas and adds Strict option
* release 0.5.4
Fix null ObjectId in createObject() and modifyObject()

(Because typeof null === 'object' returns true)
It would try to access ._id of a null object which would throw a TypeError.
Added parenthesis to follow this project's code format
* updated contributors
* release 0.5.5
Merge remote-tracking branch 'upstream/master'