stop python setup.py test from running tests twice
distutils / setuptools test.suite seems to discover tests automatically,
importing test submodules at the top of gratelpy.tests.__init__ runs them twice
moved those imports into test.runtests() so that bin/gratelpy_test can still
invoke runtests() properly
Add minimal gratelpy_test call to travis testing
After a weird problem on my computer with calling gratelpy_test
I decided to add an option to call runtests for a minimal, quick
set of unit tests that can easily be called from gratelpy_test when
run on Travis CI. By default gratelpy_test still runs the full set
merge latest changes from develop