Using py.test instead of nose

[ocefpaf]

First step to close #173

@BibMartin or @themiurgo please... 😸

[BibMartin]

Wow ! This looks good (and big amount of work).
Globally I'm okay. But I'm much too ignorant about travis to be confident for merge.

[ocefpaf]

So lets break it into pieces to make it easier to discuss.

• We had 30 tests and the are all passing in the new framework 🎉
• I removed the Jinja2 version constraint ==2.7.2 so we can test with the latest version and avoid surprises.
• We no longer support distutils. setuptools is a requirement now.
• Inside travis.yml and setup.py I am reading the requirements from requirements.txt. In the future I want to have requirements-extras.txt (with: pandas, vincent, geopandas, etc), and requirements-dev.txt (the testing stuff: mock and pytest). That way we will have only one 3 places to look for the dependencies instead of writing them on .travis.yml, setup.py, and the req files.
• I cleanup setup.py a little bit and added the test class (so we can run python setup.py test)
• nose is gone! I tweaked the tests to have the same prefix (test_something.py) and changed the classes names so pytest can discover them. The data path is now absolute, so we can run the tests from any directory.

In the future I want to break the current tests into their own files (teat_line.py, test_marker.py, etc). I know it sounds like an overkill, but I want to beef up the tests a lot to avoid regressions, and with the monolithic file we have it will be a nightmare.

[BibMartin]

@ocefpaf Thanks for explainations.

I was a bit frightened by my ignorance on travis ; but the tests pass and we don't ask more in this PR.