BREAKING CHANGE: Now AVertex, AEdge, AVertexProperty are
based on GValue type, instead of GraphSON Value. This is for
taking care of possibly nested GraphSON-encoded values in a generic
way.
BREAKING CHANGE: parseOneValue, parseListValues,
parseNonEmptyValues functions now require FromGraphSON
constraint, instead of FromJSON, because property types of
AVertex etc have changed.
Add Cardinality type and its enum instances.
Add KeyValue type and (=:) operator.
(internal change): PropertyMapGeneric is now based on
HashMap.Strict.