Update release publishing workflow to generate universal wheels

[edmorley]

1) Enable universal wheel creation by default.

This saves having to pass --universal when creating wheels: http://python-packaging-user-guide.readthedocs.org/en/latest/distributing/#universal-wheels

2) Update the publishing instructions to use twine and generate wheels.

The official Python packaging guidelines recommend using twine: http://python-packaging-user-guide.readthedocs.org/en/latest/distributing/#upload-your-distributions

This avoids sending passwords over HTTP (when using Python <2.7.9) and has a few additional advantages: https://github.com/pypa/twine#why-should-i-use-this

These instructions now also result in a wheel distribution being generated and uploaded to PyPI alongside the source distribution, which offers several advantages over it for compatible versions of pip: http://python-packaging-user-guide.readthedocs.org/en/latest/distributing/#wheels

[kumar303]

Thanks!

I think it would be fine to add twine to requirements/dev.txt and then remove the instruction to install it. There is already a prerequisite in the developer docs to install these deps.

[edmorley]

PR updated, thanks for the feedback :-)

[kumar303]

ok, looks good

[edmorley]

Thanks :-)