Pyxdameraulevenshtein

* Specifying minimum version numbers in `pyproject.toml` and `setup.py`.
* Compiled with Cython 0.29.5.

* Using the `pyproject.toml` standard set forth in [PEP 518](https://www.python.org/dev/peps/pep-0518/), NumPy will now be correctly installed as a dependency prior to running `setup.py`.

* Fixing NumPy-related install error. (courtesy simobasso)
* Enabling Python 3.7 unit tests in Travis.
* Compiled with Cython 0.29.2.

* Allow tuples and lists as input. (courtesy internaut)
* Dropped support of EOL Python versions (2.6, 3.2, and 3.3). (courtesy internaut)
* Fixed a possible division-by-zero exception. (courtesy internaut)
* Fixed a formatting error in an exception message. (courtesy internaut)
* Compiled with Cython 0.27.3.

* Clarified that this implementation is of the [optimal string alignment distance algorithm](https://en.wikipedia.org/wiki/Damerau%E2%80%93Levenshtein_distance#Optimal_string_alignment_distance) (see [this issue](https://github.com/gfairchild/pyxDamerauLevenshtein/issues/6) for more information).
* Renamed `damerau_levenshtein_distance_withNPArray` to `damerau_levenshtein_distance_ndarray` and `normalized_damerau_levenshtein_distance_withNPArray` to `normalized_damerau_levenshtein_distance_ndarray`.
* Cleaned up `np.ndarray` type and dimension checks.
* Simplified NumPy functions using [`np.vectorize`](https://docs.scipy.org/doc/numpy/reference/generated/numpy.vectorize.html).
* Hardened unicode conversion using [Cython's recommendations](http://docs.cython.org/src/tutorial/strings.html#accepting-strings-from-python-code).
* Compiled with Cython 0.24.1.

* [mittagessen](https://github.com/mittagessen) fixed a bug in `setup.py` that assumed NumPy was installed in [this PR](https://github.com/gfairchild/pyxDamerauLevenshtein/pull/5).