password-hash: add Base64ShaCrypt

[SteelAlloy]

base64ct recent versions introduces Base64ShaCrypt, a Crypt variant for sha1_crypt, sha256_crypt, sha512_crypt, and md5_crypt.

I added this variant in the Encoding of password-hash.

pub enum Encoding {
    B64,
    Bcrypt,
    Crypt,
    ShaCrypt,
}

This change is necessary to support these algorithms. (incoming PR for these once this is merged)

I only updated password-hash's Cargo.toml file and not the global Cargo.lock since there were a lot of dependencies on it. I didn't want this PR to be gigantic.

[tarcieri]

This is unfortunately a breaking change as Encoding is not marked #[non_exhaustive].

We can add it in the next breaking release of password-hash (and perhaps also mark it as #[non_exhaustive] to permit future additions in a non-breaking manner)

[SteelAlloy]

I agree with the addition of #[non_exhaustive] 👍