Adding Hankel serialization methods + unit tests for Serializer

examples/3.pautomac_light.train.json

examples/3.pautomac_light.train.yaml

examples/automaton_io.py

examples/json_save.ipynb

examples/simple_automata.json.gv.pdf

examples/simple_automata.yaml.gv.pdf

splearn/automaton.py

splearn/hankel.py

splearn/serializer.py

splearn/tests/datasets/simple_example.json

splearn/tests/datasets/simple_example.yaml

splearn/tests/test_serializer.py