[WIP] refactor: use C libcbor instead of msgpack cbor

[grzuy]

Closes #63

Blocked by PJK/libcbor-ruby#6

• Fix tests
• Update docs with new system lib prerequisite

Related cedarcode/cose-ruby#43

[grzuy]

FWIW, some (if not all) issues we're seeing in this PR are related to PJK/libcbor-ruby#5.

[bdewater]

One concern I have here is that having to install libcbor separately is not great. It breaks the "just run bundle install and you're done" workflow we have now.

It would be nice if we can package the library with the gem or provide pre-installed binaries like https://github.com/cowboyd/libv8

[grzuy]

Yes, I agree it is not ideal to add a sys level dependency.

It would be interesting to explore that possibility of packaging or providing binaries. If we do that, I'd consider first proposing that change to the libcbor gem. That's really were the dependency is coming from.

[grzuy]

Closing for now.
Same reason as in cedarcode/cose-ruby#43 (comment).