Try installing requirements before deploying (because the requirements that tox installed aren't available to the Python that Travis PyPI uses for deployment). Ref #934.

Bundle dependencies instead of vendoring them

Update Python versions

Fix certifi fallback is not used on Windows.

Fix GitHub typo

Python 3.6 is out

[CI skip]

Remove installation instructions from the README and instead refer to the Python Packaging User's Guide, which indicates to use pip for installing setuptools. Moved Credits to the history section of the documentation. Cleaned up hyperlinks.

Fix broken link in docs/developer-guide.txt

Document use of environment markers in extras_require

PEP 496 is a draft that was never accepted, so it does not have the
correct information.