Misc improvements (PRF#7)

[Vogeltak]

This PR follows on #38. It includes additional changes and improvements from our internal mirror.

• Version enum for use in getInfo
• Add CTAP2.1 fields that were missing (userSelected, enterprise attestation, large-blob key)
• Alias allowCredentials to allowList for legacy Android devices where hybrid requests where transcribed incorrectly
• Make PublicKeyCredential outputs equatable in Swift
• Update README and fix typos