Add other methods

[tresoldi]

There is a handful of methods that could be added, considering their potential in philological studies. These are (not considering alignment ones):

• Hamming (easy to add, could be good as a baseline)
• Python's various difflib.ratio (could be the fastest ones)
• Osamu Gotoh (1982) affine gap (could be used as a generic alignment one)
• Longest Common SubSequence Similarity (perhaps not so useful, but trivial to implement)
• Running Length Encoding (an additional compression method, that might be easier to explain/demonstratet -- no point in implementing the Burrows-Wheeler transform, though)
• Square Root NCD (additional compression method)
• Tversky index (additional token method, but only makes sense after properly integrating ngrams)
• Overlap coefficient (additional token method, but only makes sense after properly integrating ngrams)
• Tanimoto distance (additional token method, but only makes sense after properly integrating ngrams)
• Cosine similarity (additional token method, but only makes sense after properly integrating ngrams)
• Monge-Elkan (additional token method, but only makes sense after properly integrating ngrams)
• Bag distance (additional token method, but only makes sense after properly integrating ngrams)