* Much more Pythonic API for modifying Structure/Molecule species. Now,
strings, slices, and sequences should magically work, in addition to the
previous API of simple int indices. Examples::
s[0] = "Fe"
s[0] = "Fe", [0.5, 0.5, 0.5] Replaces site and fractional coordinates.
s[0] = "Fe", [0.5, 0.5, 0.5], {"spin": 2} Replaces site and fractional coordinates and properties.
s[(0, 2, 3)] = "Fe" Replaces sites 0, 2 and 3 with Fe.
s[0::2] = "Fe" Replaces all even index sites with Fe.
s["Mn"] = "Fe" Replaces all Mn in the structure with Fe.
s["Mn"] = "Fe0.5Co0.5" Replaces all Mn in the structure with Fe: 0.5, Co: 0.5, i.e.,creates a disordered structure!
* Massive update to internal representation of Bandstructure objects for
memory and computational efficiency.
* Bug fixes to CIF parsing in some edge cases. (Will Richards).