Feature name for `password-hash` functionality: stick with `simple`?

[tarcieri]

All of the crates in this repo provide a low level API for key derivation functions, as well as a high-level API for working with password hash strings (either PHC or MCF, and soon hopefully both for some constructions).

Right now most crates call this feature simple. The name has some precedent, but may not be completely intuitive for some users.

balloon-hash just calls the feature password-hash after the password-hash crate, which also makes sense.

Should we continue using the simple name, or is password-hash a better name? Whatever we do, it should be consistent across all crates.

[newpavlov]

Since password-hash is much simpler after the recent changes maybe it's worth to remove the feature completely?

If we are to keep it, I am fine with switching to password-hash.

[tarcieri]

Allowing it to disabled will remove at least three dependencies per crate: password-hash, base64ct, and at least one of mcf or phc.

Users who only depend on KDF functionality probably do not want the extra dependencies.