Takes care of multiple oxidation states for an element in a structure. Also coordination number is used as input to ionic radius calculation

When generating the voronoi nodes, a single ionic radii  was used for each species in the structure.
Now, when multiple oxidation states of a single species are present in the structure, different ionic radii for different oxidation states are used.  

Also, coordination number is used as input to compute the ionic radius. The file ionic_radii.json contains Shannon's ionic radii database for most of the elements. Data is missing for lanthanide, actinides and for 7th row elements. 

Bharat