MinHash retrieval by key

[DavidNemeskey]

Hi,

I see that in #233, a way was proposed to retrieve the minhash associated to a key. I can also see that it has been implemented in #234, although I cannot find the described method in 1.6.5 (only get_minhash_hashvalues; is that intentional?).

It would be great if a similar method could be added to the other LSH objects, such as the default MinHashLSH, for much of the same reasons. Thanks!