Set up unit tests/continuous integration

[aimalz]

I'm (sorta) familiar with Travis CI, but I think @pennalima mentioned something else in today's call, so I'm assigning both of us to set this up.

[pennalima]

Hi @aimalz,
We use the glib tools to build the unit tests of NumCosmo.
Besides, NumCosmo repository is hooked to Travis CI, such that each commit is built ans the
tests are run.