Add 'make test' target to Makefile for running unit tests.
Add 'make test' target to Makefile for running unit tests.

This uses nosetest, and hopefully discovers all the required modules.
We may want to replace it with a special test.py file for more control,
or running example cases, but this seems to work for now.
pierrelb/RMG-Py,comocheng/RMG-Py,KEHANG/RMG-Py,enochd/RMG-Py,nickvandewiele/RMG-Py,nickvandewiele/RMG-Py,chatelak/RMG-Py,enochd/RMG-Py,chatelak/RMG-Py,KEHANG/RMG-Py,pierrelb/RMG-Py,comocheng/RMG-Py,faribas/RMG-Py,nyee/RMG-Py,nyee/RMG-Py,faribas/RMG-Py