Add the Cadence Language

**What programming language should we add?**
Cadence - the Smart Contract programming language for the Flow blockchain.

**What is the official website for the language?**
https://docs.onflow.org/cadence/

**Is this a language that comes in many variants? If so, which variant should we support?**
No.

**Does the language have an official logo?** If so

- please include a link to an example
This is the Flow blockchain logo, which is also used for Cadence:
https://www.google.com/search?q=flow+logo&tbm=isch&ved=2ahUKEwjiv4Gq8e70AhVvn3IEHcNLCbUQ2-cCegQIABAA&oq=flow+logo&gs_lcp=CgNpbWcQAzIECAAQQzIFCAAQgAQyBQgAEIAEMgUIABCABDIFCAAQgAQyBQgAEIAEMgQIABAeMgYIABAFEB4yBggAEAUQHjIGCAAQBRAeOgYIABAHEB46BggAEAgQHjoICAAQgAQQsQM6BwgAELEDEEM6CwgAEIAEELEDEIMBOgoIABCxAxCDARBDOgQIABADUPkIWKkOYJEQaABwAHgAgAFPiAGxBJIBAjEwmAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=HqK-YeK4KO--ytMPw5elqAs&bih=937&biw=1920&rlz=1C1GTPM_enUS828US828#imgrc=wW9ufA26Xer-QM

- please list the attribution rights of that logo
This logo is owned by the Flow team (https://twitter.com/flow_blockchain).

**Is there a testing framework available for the language?**
Yes, you can mess around with Cadence code on the Flow playground here: https://play.onflow.org/

**If it is not supported by Highlightjs, what is the closest supported language it maps to?**
It is not officially supported, likely because this language is still relatively new and is also a part of the Blockchain space, which has not seen wide adoption yet. Although I do see Solidity is listed there.

It is closest to the Swift programming language.

**Who will be leading the effort to launch the track?**
Jacob Tucker (me) and a Decentralized Autonomous Organization (DAO) that is operating to educate members of the Flow community. The DAO acts as a community of people who will continuously produce content to help out in this effort.

The issue provides no repository files or tests to start from. Read the Cadence documentation and try the Flow playground first; done would require an agreed implementation path for adding Cadence support to this track.

Written by the indexing model from the issue text.