Teleport 0.3.0 released (Python)

[Alexei Boronine]

This is a complete rewrite of the Python implementation to match the new spec [0], which has been submitted as a Internet Draft. This includes brand new documentation [1], a common test suite [2], several recipes from the documentation are included in the `teleport.examples` module, including Nullable, a type proposed by Cyril in an earlier discussion. This version adds support for Python 3.

Short-term roadmap:

1. Make some adjustments to the spec (e.g. rename Float to Decimal)

2. Rewrite JavaScript port, minimal implementation for now

3. Port Cosmic [3] to Teleport >=0.3

[0] https://datatracker.ietf.org/doc/draft-boronine-teleport/?include_text=1

[1] http://teleport-json.org/python/0.3/

[2] https://github.com/cosmic-api/teleport/tree/master/_test

[3] http://cosmic-api.com/