ctap-types maps the various types involved in the FIDO CTAP protocol
to Rust structures consisting of heapless data types.
We currently follow the non-public editor's draft dated 19 March 2019.
It still uses FIDO_2_1_PRE to signal new commands, but uses non-vendor
API numbering (e.g. 0xA for credential management).
It also contains a lightweight CBOR deserializer, as the existing serde_cbor
creates very large code.
The various transport protocols (USB, NFC, BLE) are expected to handle low-level protocol details and deserialize requests / serialize responses, so the authenticator logic is decoupled from these details.