fix docs of group_structures function
Fix extremely serious bug in behavior of DummySpecie.
Did not implement __hash__, which leads to bad comparisons.
Also, Site and PeriodicSite did not support from_dict for DummySpecie.
Merge branch 'master' of github.com:materialsproject/pymatgen
Merge branch 'master' of https://github.com/davidwaroquiers/pymatgen
REvemo add_oxidation state by site fraction for now.
Update dev docs
Documentation updated for bond_valence of unordered structures