Adding Python 3.7 support

[mwysokin]

Is there any work going on in order to allow using kazoo with Python 3.7?

[StephenSorriaux]

Hi,

There is not ay work going on but it seems to me that adding this would be easy. Feel free to submit a PR if you have some times on your side. If not, I will try to find a moment for this.

[jimbobhickville]

Just curious, what doesn't work with python 3.7 right now? I ask because we're using kazoo in a py37 project and seeing some weirdness with things like custom listeners never receiving CONNECTED events and some oddness around expired sessions. Wondering if that's related.

[ninowalker]

+1 - is there anything known to be broken or incompatible with 3.7? Python 3.7 is now almost one year old since the official release.

[dwo]

It looks like some work has been done already eg. 225d336