Updated py-setuptools to 21.0.0.

v21.0.0

02 May 2016

    Removed ez_setup.py from Setuptools sdist. The bootstrap script
    will be maintained in its own branch and should be generally
    be retrieved from its canonical location at
    https://bootstrap.pypa.io/ez_setup.py.

v20.10.0

25 Apr 2016

    #553: egg_info section is now generated in a deterministic
    order, matching the order generated by earlier versions of
    Python. Except on Python 2.6, order is preserved when existing
    settings are present.
    #556: Update to Packaging 16.7, restoring support for deprecated
    python_implmentation marker.
    #555: Upload command now prompts for a password when uploading
    to PyPI (or other repository) if no password is present in
    .pypirc or in the keyring.

(wiz)