Test on pypy3

Adapt resolution of classes from importlib.machinery. Restores compatibility for PyPy3 where importlib.machinery exists but FileFinder and SourceFileLoader aren't implemented.

Rather than re-use globals of setuptools.launch, build a unique namespace in which to launch the script. Prevents imports from occuring relative to 'setuptools' on Python 2. Ref #490.

Also hide Cython when hiding setuptools, as setuptools will have imported Cython and Cython references the distutils.Extension. Fixes #488.

Remove JythonCommandSpec as it's not required on Jython 2.7 and setuptools no longer supports anything 2.5, but had to test for 'Jython on Windows' in two other places

Relicense the package as MIT license. Drop licensing as PSF and Zope as neither of those licenses grant authority for use outside their respective projects. Vendored projects are licensed under their respective licenses, currently MIT for six and Apache v2 for packaging. Fixes #132.

Merged in svetlyak40wt/setuptools/svetlyak40wt/make-194-same-level-header-as-other-vers-1453106898145 (pull request #171)

Make 19.4 same level header as other version numbers.

Invoke import on importlib.machinery directly. Access an attribute to force import in delayed-import environments. Fixes #487.

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branch : svetlyak40wt/make-194-same-level-header-as-other-vers-1453106898145

The problem was that restructured text considered 19.4 is a sibtitle to "CHANGES".

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branch : svetlyak40wt/make-194-same-level-header-as-other-vers-1453106898145

Possible fix for #207