Bunch of missing / unexposed features in ethers-ens

[Amxx]

Please consider:

• adding the setName method (already in the SetNamePlugin) to the help/usage screen
• adding a feature to register/setResolver for reverse names (through the reverse registrar)
• adding lookup function to read text entries (that have been set with --set-text) through the cli

Thank you :)

[Amxx]

register reverse names: ethers-io/ethers.js#1110

[Amxx]

lookup functions: ethers-io/ethers.js#1111