argon2 v0.3.0

[tarcieri]

Added

• alloc feature (#215)
• Params now supports keyid and data fields (#216)

Changed

• Argon2::new now has explicit version and params (#213)
• Factored apart Argon2::new and Argon2::new_with_secret, making the
  former infallible (#213)
• Params struct is now opaque with field accessors, and ensured to
  always represent a valid set of parameters (#213)
• Removed version parameter from hash_password_into, using the one
  supplied to Argon2::new (#213)
• Bump password-hash to v0.3 (#217, RustCrypto/traits#724)
• Use resolver = "2"; MSRV 1.51+ (#220)

Removed

• Params no longer has a version field (#211)