Flatdict2

- FIXED List Flattening does not return list when an odd number of depth in the dictionary (27 [mileslucas](https://github.com/mileslucas))
- CHANGED FlatterDict to allow for deeply nested dicts and lists when invoking `FlatterDict.as_dict()` (28 [mileslucas](https://github.com/mileslucas))
- Flake8 cleanup/improvements
- Distribution/packaging updates to put metadata into setup.cfg

- FIXED `FlatDict` behavior with empty iteratable values
- CHANGED behavior when casting to str or repr (23)

- Add 3.7 to Trove Classifiers
- Add Python 2.7 unicode string compatibility (22 [nvllsvm](https://github.com/nvllsvm))

- CHANGED `FlatDict.as_dict` to return the nested data structure based upon delimiters, coercing `FlatDict` objects to `dict`.
- CHANGED `FlatDict` to extend `collections.MutableMapping` instead of dict
- CHANGED `dict(FlatDict())` to return a shallow `dict` instance with the delimited keys as strings
- CHANGED `FlatDict.__eq__` to only evaluate against dict or the same class
- FIXED `FlatterDict` behavior to match expectations from pre-2.0 releases.

- FIXED metadata for pypi upload

- Code efficiency refactoring and cleanup
- Rewrote a majority of the tests, now at 100% coverage
- ADDED `FlatDict.__eq__` and `FlatDict.__ne__` (13 - [arm77](https://github.com/arm77))
- ADDED `FlatterDict` class that performs the list, set, and tuple coercion that was added in v1.20
- REMOVED coercion of lists and tuples from `FlatDict` that was added in 1.2.0. Alternative to (12 - [rj-jesus](https://github.com/rj-jesus))
- REMOVED `FlatDict.has_key()` as it duplicates of `FlatDict.__contains__`
- ADDED Python 3.5 and 3.6 to support matrix
- REMOVED support for Python 2.6 and Python 3.2, 3.3
- CHANGED `FlatDict.set_delimiter` to raise a `ValueError` if a key already exists with the delimiter value in it. (8)