Added Python 2 and 3 compatibility

Package now works w/ Python 2.7, 3.4, 3.5, 3.6

• All tests pass, except one test that is related to an underlying bug in a dependency (see TODO in test module for more info).

Initial Test Suite Complete

As this is a port of the apollographql subscription libaries, this release brings the repo up to date with the extensive test suites contained in apollographql subscription-transport-ws v0.5.3 and graphql-subscriptions v0.3.0