Add tests and enable travis

[msullivan]

The tests (and a bunch of the config) is pulled in from mypy

[msullivan]

The travis was tested on my fork at https://travis-ci.org/msullivan/mypy_extensions, but needs an admin to enable it on the python org.

[ilevkivskyi]

Thanks! You can either merge this version, or try the typing settings (I would prefer the latter, but this not a strong preference).

[ilevkivskyi]

Since this is a "runtime" package, I would rather use the Travis settings from python/typing.

[msullivan]

Which things from typing do you prefer? Is it just running on a bunch more versions, or do you want to not use tox?

[ilevkivskyi]

Actually both (but first is probably more important).

[msullivan]

What's the reason to avoid tox? (I don't have any real opinion one way or another except that the tox version works already :P)

[ilevkivskyi]

I just don't want to learn something the need for what I don't understand. But since it already works, then OK.

[ilevkivskyi]

I just don't want to learn something the need for what I don't understand. But since it already works, then OK.