Consider exposing an additional simplified interface matching traditional sign/verify

[dlongley]

This additional interface would receive data to be signed / verified as a string of bytes (using Uint8Array) that contain serialized parameters such as header, messages, etc. using the serialization primitives defined by the BBS spec. Doing so would adhere to existing interfaces that already work with / plug into APIs such as WebKMS without the need to invent a new interface.