Multihash -> string in Solidity

[decafboba]

Hello @saurfang! Thanks for this contribution, it has been super useful!

One thing I have been wanting to try is to take in a Multihash as an input parameter and convert it into a string.

My main reasoning for doing this is, so it can be set to the value in ERC721's tokenURI(), which is of type string. Although there is examples of going to and from Multihash <-> string in the JavaScript, I think quite a few folks would love to know how to do this in Solidity.