Minor inconsistencies in API naming

[faassen]

While you create an RsVec from a bit vector using from_bit_vec, the BpTree is created using from_bit_vector. Perhaps from_bit_vector can be deprecated in favor of from_bit_vec?

[faassen]

I also noticed it's SparseRSVec and not SparseRsVec, while it's RsVec.

[Cydhra]

Relates to #9

[Cydhra]

The deprecation for the top one could be done. Whether a second deprecation for correcting the capitalization is useful, I don't know. When I push a 2.0 update, downstream crates will need major updates anyway to migrate, so I think the deprecations aren't very useful in both cases.

I noticed the wrong capitalization about 5 minutes after I released the 1.6 update. I was very annoyed :P