Create slither-interface

[montyly]

See #1802 (comment)

[0xGusMcCrae]

I'll take a look at this over the weekend and see if I can get it done

[montyly]

That's great @0xGusMcCrae, let me know if you need guidance or help.

Some notes:

• We can build slither-interface following the tool's demo structure: https://github.com/crytic/slither/tree/master/slither/tools/demo
• Most the logic might already be implemented in slither/utils/code_generation.py
• We recently made a significant refactor of our testing strategies. Be sure to work from the dev branch, and read https://github.com/crytic/slither/blob/dev/CONTRIBUTING.md

[0xGusMcCrae]

I've got the basic functionality down. I just need to write some tests and I should have a PR ready tomorrow.

For the output, do we want to print the interface in the console and allow users to write to file manually?

i.e. slither-interface WETH9 0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2 >> IWeth9.sol

Or should it write to file by default? Maybe a flag so there's an option between the two?

[montyly]

Awesome. I think a file is probably more appropriate.

Most of our tools use crytic-export/name_tool/contract, maybe we can do crytic-export/interfaces/ContractA.sol, crytic-export/interfaces/ContractB.sol, ... by default?