Representation: most_similar, closes #45

[henrifroese]

• add function most_similar in representation.py

Only a draft at the moment; no tests yet.

*EDIT: *

Interested in opinions concerning the "function design"! It currently has signature

most_similar(
    s: TextSeries,
    s_represented: Union[VectorSeries, RepresentationSeries],
    vector: List[float],
    max_number=None,
) -> TextSeries:

and works e.g. like this:

    >>> import texthero as hero
    >>> import pandas as pd
    >>> s = pd.Series(["I like football", "Hey, watch out", "I like sports", "Cool stuff"])
    >>> s_pca = s.pipe(hero.tokenize).pipe(hero.tfidf).pipe(hero.flatten).pipe(hero.pca) # TODO: remove flatten when pca is updated w.r.t. Representation Series
    >>> # want to find the two most similar to "I like football", which has index 0
    >>> s_most_similar = hero.most_similar(s, s_pca, s_pca[0], max_number=2)
    >>> s_most_similar
    0    I like football
    2      I like sports
    dtype: object

[henrifroese]

Put on hold until Series Types are figured out.

[henrifroese]

• maybe use cosine distance by default; add argument to choose function
• maybe change signature to most_similar(s: TokenSeries(?), text, representation_function, metric)
• maybe prepare tutorial for users instead of adding function to TextHero