implement continuous integration #211
Description
It looks like this bug #126 (comment) would have been caught by this test https://github.com/SuLab/mark2cure/blob/master/mark2cure/task/entity_recognition/tests.py#L80, but presumably wasn't because we don't have automated testing in place. Assuming my diagnosis is correct (and possibly even if it isn't) we need to get CI up and running so we can more easily diagnose and prevent bugs.