New Command: Fetch interface declaration from etherscan.io

[tintinweb]

Implement a new command .fetch interface that auto-generates and loads interface declarations from etherscan.io.

• command: .fetch interface <address> <interfaceName> [optional: chain=mainnet]
• Tries to fetch the contract ABI from etherscan.io; may fail if not available or etherscan rate limits us
• generates solidity interface declaration from ABI via abi-to-sol
• prints and makes the downloaded interface available in the REPL

e.g. when using ganache in fork mode this allows you to easily interact with the contract.

Example:

.fetch interface 0x40cfEe8D71D67108Db46F772B7e2CD55813Bf2FB Test
Test t = Test(0x40cfEe8D71D67108Db46F772B7e2CD55813Bf2FB)
t.symbol()