Add distance metric: Tanimoto variant of Jaccard score

[vickumar1981]

Add an implementation for the tanimoto variant of the jaccard distance/score.

https://en.wikipedia.org/wiki/Jaccard_index#Tanimoto_coefficient_(extended_Jaccard_coefficient)

Note: For the tanimoto algorithm, the score is unnecessary b/c it will/outhgt to be the same as the jaccard score - the distances should be different.

[vickumar1981]

Addressed by: #13