Add Swift DAG-CBOR Library

[thecoolwinter]

Adds my Swift CBOR library to the test suite. Only requires a Swift installation, works on Linux so it won't restrict the run script to macOS. The test harness is a simple Swift executable, and I wrote it so it should be very easy to add more Swift implementations if needed. I also quick updated the README to reference the update_libs.sh script instead of instructions for npm install.

I've also gone ahead and added Swift to the CI jobs to ensure there's no extra work on y'alls side to get that set up!

• Updated the update_libs.sh script.
• Updated the super_harness.sh script.

[makew0rld]

Sorry for the delay on this. LGTM, thanks for adding. Note your library does fail one important test, "valid CID with short tag". That's not a blocker for the test suite but it might be something you want to look into.

One thing I am concerned about is the lack of error messages, for example clicking a passing invalid_in test shows this:

{
  "error": null,
  "output": null,
  "pass": true
}

But ideally it would show the nature of the error.

Not a blocker, but if you could improve this in a future PR that would be great.

[makew0rld]

Ok additionally, I think some of the implementation is wrong.

• invalidDecode should only test the decoder
• invalidEncode should decode the data using a third-party neutral (not dag-cbor or DASL) CBOR decoder, and then try to encode that object
• Your roundtrip function looks right

Also the library version shouldn't be hardcoded.

A good reference harness for you to look at is harnesses/go-dasl/main.go, but you can look at any you like.