First set of unit tests; for nntools.objectives

Found a bug in nntools.objectives.crossentropy (no return value).

To run tests, first install necessary requirements with:

  python setup.py dev

Then run:

  py.test

(These are assuming you've activated your virtualenv.)
Woops, I meant to remove this as part of #28; it's not needed anymore.
Add unit tests for nntools.init.
Add experimental Travis configuration
Cosmetics
Merge pull request #36 from dnouri/test-objectives

Test nntools.objectives + nntools.init + Travis configuration