New average similarity method

[marco-2023]

This PR should close (for now) the implementation of n-ary similarity methods.

Addressed problems

1. Added support to the Instant Similarity ( isim)
   • Implemented support for Instant Similarity (isim) methods within the NSimilarity and SimilarityIndex classes.
   • The previous method for calculating average similarity is now called Extended Similarity ( esim) and is supported for "backward compatibility?"
2. Added support for esim and isim to utilize a p-norm average similarity.
3. Added tests for the isim method with the different similarity indexes and p-norm averages using reference data generated by Ramón's group code

Remaining things to do (future)

1. We don't have a source of reference data for esim with p-norm averages different than 1.
2. Improve docstrings format

Notes: After this is merged, the Quickstart notebook (PR #186) can showcase the new flexibility of the methods.