Migrate to Pytest - #527

CI is green.

What do you think about this @mfeurer @janvanrijn ?

So, pip install is now the recommended way to install packages (even local packages) as compared to python setup.py install (see https://packaging.python.org/tutorials/installing-packages/#installing-from-a-local-src-tree).

pip install .  # dot important at the end

installs the local package.

To get the behavior of develop, it's necessary to add the -e flag.

And to install extra dependencies, one would do,

pip install openml[test]

which installs extra "test" dependencies specified in the setup.py. So the sum of that in this case is,

pip install -e .[test]

with some parenthesis as I wasn't sure how bash would handle it.

Thanks a lot for explaining this. I just talked to @janvanrijn and he's okay with merging this. Thanks a lot!

Thanks for the review @mfeurer !