Auto-Generate abis from a github url folder and expose them through repl

[nicosampler]

I think it would be awesome if eth-cli provides a functionality to receive a github url to the "contracts folder" and auto-generate the abis for the contracts in that url. Then it will expose those abis to be used in repl mode, as the ERC20 does.

It would save a lot of time when you need to interact with a contract that you do not own.