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* NdbConnectionField added arguments that can be used in quert:
* keys_only - to execute a keys only query
* batch_size - to control the NDB query iteration batch size
* page_size - control the page sizes when paginating connection results
* Added support for LocalStructuredProperty.
* Given a property `ndb.LocalStructuredType(Something)` it will automatically
map to a Field(SomethingType) - SomethingType has to be part of the schema.
* Support for `repeated` and `required` propeties.