Add support for releasing Python 3 wheels #7197
The final step in #6062 is to add support for releasing Pants and its contrib packages as compatible with Python 2.7 and 3.6 and 3.7. Specifically, universal wheels should be marked as
This resolves the wheels portion of #6450.
Note we still cannot release a Python 3 compatible PEX, which is blocked by pantsbuild/pex#654.