* Upgraded to Frogfish.

* Adds compatibility with frogfish + updated README.md for installation
* Switched from edgetpu API to tflite_runtime + pycoral API
* Added unit test with utilities for visualizing new results vs reference results

Test:
$ python3 posenet_engine_test.py
For visualizing/comparing model results to reference file:
$ python3 test_utils.py --visualize_model_results --visualize_reference_results
For writing new reference file:
$ python3 test_utils.py --write_csv

* Fixed indentation

* Fixed pretty printing.

* clean up.

* Added TODO for window/mac supports