Use enum-compat instead of enum34 directly

[jeanregisser]

Hi,

I'm getting an error in Home Assistant running python 3.6 that uses your library: AttributeError: module 'enum' has no attribute 'IntFlag'

It appears enum34 is not meant to be installed in Python versions 3.4+
so this fixes it.

Let me know what you think,

[balloob]

I would love to see this PR get merged. It doesn't contain any breaking changes and makes sure modern versions of Python can be used with this lib.

From the https://github.com/jstasiak/enum-compat README:

This is a virtual package, its whole purpose is to install enum34 on Python older than 3.4. On Python 3.4+ it’s a no-op.

[peplin]

Thanks!