Updates to Instance
 - Fixes an error when saving instances without custom change sets
 - Adds a `document` virtual property which returns the backing document from the database
 - Adds a `select` function which allows you to easily select array/object values based on
   a selector function (makes working with arrays containing documents easier)
 - Adds a `first` function which does the same as select, but only returns the first result.
2.10.0