general: stack

* coveralls
* travis
* sphinx
* tox
* pytest

EDIT: changed to pytest

Signed-off-by: Mateusz Susik <mateusz.susik@cern.ch>
> BSD is not contemplated.

... but there are clauses allowing the use of other licences in special cases, e.g. to integrate in an existing FOSS ecosystem, which we used for BSD-ifying our Flask extensions.  (Confirmed by @TimSmithCERN who has the role of CERN FOSS licensing officer/advisor.)

> Is there a reason why we are not simply picking up GPL3 as per the official CERN mandate?

IIRC @glouppe would prefer BSD over GPL, hence my above-mentioned thoughts on when this might be feasible.  E.g. I assume Beard would use scikit-learn heavily?