Fixes #811. Fixes reflinks
fixed bug for queryset.distinct to work also on embedded documents, not just on lists of embedded documents
implemented ability to return instances and not simple dicts for distinct on subdocuments
added test for capacity to get distinct on subdocument of a list
Added a test that verifies distinct operations on nested embedded documents.
fixed order of list for the test to pass
Added EmbeddedDocumentListField Implementation

- Added new field type: EmbeddedDocumentListField.
- Provides additional query ability for lists of embedded documents.
- Closes MongoEngine/mongoengine#503.
UnitTests for EmbeddedDocumentListField
Updated Docs to include Embedded Document Querying