Ensure all hash keys are unicode

Signed-off-by: Byron Ruth <b@devel.io>
Change serialization to use a breadth first method

Given a node, find all neighbors first followed by their relationships.
Iterate over each neighbor and follow the same pattern.
Add support for batching nodes and rels in serializer

Each batch contains either a set of nodes or rels. The rels batches
are always ordered after it's dependent nodes and is primarily useful
for parsing and importing in supported backends such as Neo4j.