increase coverage

mostly by omitting coverage of things that shouldn't be tested anyway
(e.g. debugging functions only run if __name__ == "__main__"
Merge branch 'master' of github.com:pele-python/pele into coverage
further increase coverage

add new tests for heat_capacity.py and for permutational alignment with
munkres
move soft sphere potential to playground

I think no one was using it and it wasn't tested or documented
fix some bugs in get_thermodynamic_information

The bugs were about dealing cleanly with exceptions raised by the child
processes
add some tests for disconnectivity graph
Merge pull request #71 from js850/coverage

increase coverage and add some tests