Renames test to tests

* Renames `test` directory to `tests` as is the usual practice.

Signed-off-by: Tibor Simko <tibor.simko@cern.ch>
Merge pull request #2 from tiborsimko/tests

Renames test to tests

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>