Common API changes needed to (later) add caBLE support.

[micolous]

This adds functionality, changes APIs and refactors webauthn-authenticator-rs in ways that's necessary (or useful) for caBLE support (#232), without actually adding support for caBLE itself.

• AuthenticatorBackendHashedClientData: new trait for AuthenticatorBackends which accepts client_data_hash directly. This de-duplicates the client_data_json handling, and allows the library to proxy requests from a caBLE initiator.
• perform_register_with_request, perform_auth_with_request: Accepts MakeCredentialRequest and GetAssertionRequest commands directly, mapping them onto AuthenticatorBackendHashedClientData. This allows it to act as a caBLE authenticator, while also handling PIN/UV auth internally when proxying to physical authenticators (as browsers don't attempt it!)
• crypto: new module for common cryptographic operations, shared between caBLE and CTAP2 implementation.
• CTAP2:
  • implement AuthenticatorBackendHashedClientData instead of AuthenticatorBackend
  • adds serialisation for Map<u32, String> to GetAssertionResponse and MakeCredentialResponse and from GetAssertionRequest and MakeCredentialRequest for perform_*_with_request.
  • allow for both Map<String, String> and Map<u32, String> representations of CBORRequest and CBORResponse for perform_*_with_request.
  • add GetInfoResponse serialisation
  • make to_short_apdus and to_long_apdu stand-alone methods
  • Token is now mutable, and Token::close is now async
  • use short APDUs for selecting FIDO2 applet over NFC, because Feitian tokens don't support extended APDUs (in violation of the FIDO specification!)
• SoftPasskey:
  • implement AuthenticatorBackendHashedClientData instead of AuthenticatorBackend
• SoftToken:
  • implement AuthenticatorBackendHashedClientData instead of AuthenticatorBackend
  • add support for persisting the SoftToken (as SoftTokenFile)
  • add examples/softtoken for creating a persisted SoftToken
• ui: Add methods for caBLE (displaying QR codes and reporting status)
• examples/authenticate:
  • refactor to use command line arguments, rather than interactive text UI
  • re-open the connection to the key after every operation (needed for Feitian NFC keys, and also caBLE)
• clean up some dead/commented code that was from testing earlier features
• fix some documentation formatting errors

Fixes #

• cargo test has been run and passes
• documentation has been updated with relevant examples (if relevant)

[micolous]

This should be good to go now.