Add support for CBOR Diagnostic Notation

[lrosenthol]

CBOR Diagnostic Notation is a text-based syntax for working with CBOR, as described in Section 8 of the standard - https://www.rfc-editor.org/rfc/rfc8949.html#name-diagnostic-notation

It would be great to have methods for converting from CBOR binary data to CBOR Diagnostic notation, and from diagnostic notation back to CBOR.

What other libraries (C++ or other) have this feature?

None. The only ones I can find are in Ruby and Rust.

[danielaparker]

Thanks for the suggestion.