Add functions to read and write pyger data to pickle files.

- pyger/__init__.py
  - Add save_pyger_pickle() and load_pyger_pickle() to available function list

- pyger/pyger.py
  - Add definitions for save_pyger_pickle() and load_pyger_pickle().

These are intended to help the user save and reload relevant pyger data in a format that is compatible with the original data structures. These can also be used for testing of code changes by making it easier to compare results of new code against production code.