Exclude a couple of tests from test suite

These tests rely on order of keys in 'auxfns' dictionary. They fail
_sometimes_ on Python 2. And *always* fail on Python 3 due to
intentional randomness in the order of keys.
Fix 'python setup.py sdist' warnings

Convert README in reStructuredText format
[ci skip]
Set up 'tox', adjust 'pytest' settings

[ci skip]