Pyobjson

* Changed `pyobjson` key/value string delimiter and how deserialization handles it

* Improved serialization/deserialization of nested objects.

* Simplified serialization/deserialization to support arbitrary nested objects.

* Added support for serialization/deserialization of:
* functions (and other callables)
* sets
* tuples
* paths
* datetimes
* nested collections

* Refactored `pyobjson` into `base`, `data`, and `utils` modules
* Extended serialization/deserialization versatility.

* Created the pyobjson utility library for serializing/deserializing custom Python objects to/from JSON.