ENH: Python3 support

[westurner]

• Test w/ python 3.x, update as needed
• Update travis.yml
  https://github.com/westurner/pyline/blob/master/travis.yml
• Update tox.yml
  https://github.com/westurner/pyline/blob/master/tox.ini
• Release a Python 3 compatible version of pyline to PyPI (v0.3.20)
• Handle the Python 3 mixed types sorting behavior

[pahaz]

$ pyline --help
Traceback (most recent call last):
  File "/usr/local/bin/pyline", line 7, in <module>
    from pyline.pyline import main
  File "/usr/local/lib/python3.5/site-packages/pyline/__init__.py", line 8, in <module>
    __main__ = pyline.main
AttributeError: module 'pyline' has no attribute 'main'

[jayvdb]

This hasnt been released to PyPI, which is stuck on v0.3.16 while v0.3.17 has been tagged in the repo

[westurner]

This is blocking getting a pyline with Python 3 support uploaded to PyPi:
From #29 (comment) :

Python 3 fails on:

sorted(['a', None, 1])

Due to docs.python.org/3/whatsnew/3.0.html#ordering-comparisons

stackoverflow.com/a/47368476 is an implementation of Python 2-style sorting for Python 3.

• Ask for permission to use in an open source project
• get permission
• Decide how to enable or disable this feature with CLI args

[westurner]

Solution for now: ~ transform None to "":

sorted([None, "b", "c"]) -> sorted(["", "b", "c"])

sorted([None, 1, "c"]) -> sorted(["", 1, "c"])  # which still errors; but shouldn't happen without a strange type cast function

[westurner]

I just released pyline v0.3.20 with Python 3 support to PyPI: https://pypi.org/project/pyline/