Add support for Ethereum Name Service (ENS)

[jornfranke]

The Ethereum Name Service (ENS) allows registration of Internet addresses on the Ethereum blockchain. In some sense, it is similar to Namecoin for the Bitcoin blockchain, but based on the smart contract VM.

https://ens.domains/

The idea here is to add additional utility functionality and Hive UDFs to the library.
Of course, everything is supplied with an example and unit tests/integration tests.