Exclude tests folder from wheels distribution

[thibaudcolas]

Issue Summary

#107 excludes the tests folder from our source distributions, but not from wheels, which are the most commonly used format. We need to find a way to exclude tests from both distributions. packages=find_packages(exclude=["tests"]) doesn’t seem to work.

Steps to Reproduce

python setup.py sdist bdist_wheel

[zerolab]

@thibaudcolas #137 solves that issue