update mongoskin
old semver for node 0.8
provide callback for index creation (needed for write concern)
assign db to Model.db
Merge pull request #19 from paulbdavis/update-mongoskin

Update mongoskin
parse `ObjectID` strings

Fix for the recursive toJSON calling in base modella which was
converting `ObjectID`s into strings before the save method is called.

Setting `{type: ObjectID}` on an attribute will cause any string value
passed in to be parsed into an `ObjectID`.
updated to newest modella for testing
do proper checking