Move setuptools stuff from setup.py to setup.cfg

[mrg29]

This PR is analogous to this commit from obsrvbl-oss/flowlogs-reader#41.

Changes made, other than the file format:

(1) I did not carry over these lines:

    test_suite='tests',	
    tests_require=[],

Those are for running python setup.py test, which is deprecated and isn't used in the CI file.

(2) This line:

    packages=find_packages(exclude=[]),

should've been this instead:

    packages=find_packages(exclude=['tests']),

I did not carry over the exclude= part at all, but will write a separate PR that fixes it.