SimilarityEncoder cleanup

[LeoGrin]

fix #573

[LilianBoulard]

Thanks! Do you mind using this PR for some more cleanup of the SimilarityEncoder?
I'm thinking of is the similarity argument, which should be removed (along with the TODO).

[GaelVaroquaux]

I would modify the "notes" section of the SimilarityEncoder as such

"The functionality of :class:SimilarityEncoder is easy to explain and understand, but it is not scalable. It is useful only to capture links across a few categories (eg eg: “west”, “north”, “north-west”), but not when there are many categories, as with open-ended entries.
Instead, the :class:~skrub.GapEncoder is usually recommended."

[GaelVaroquaux]

Look's great to me. I've left a few comments, and in addition I agree that if you can tackle @LilianBoulard 's point its great.

Thanks!!

[LeoGrin]

I'm thinking of is the similarity argument, which should be removed (along with the TODO).

I don't see any TODO @LilianBoulard.

[GaelVaroquaux]

Two tiny suggestions. +1 to merge on my side once they have been addressed.

@LilianBoulard : I'll let you do a final review and press the merge button if everything is fine on your side.

[GaelVaroquaux]

Yes but we have a test which check that an estimator summary fits in one line.

Ah, darn such crazy rigidity.

"Encode string categories to a similarity matrix, to capture fuzziness across a few categories."

This is good