Add support for remapping.

[MicahZoltu]

My import statements leverage Solidity remapping which means they look like:

import 'ROOT/relative/path/to/other.sol

I then provide a remapping in my solc input JSON that maps ROOT to an absolute path of the root of my solidity source code.

Unfortunately, I don't see a way to provide such a remapping in this package, which means all of my imports are flagged as bad.

[willclarktech]

This is also a problem when using Truffle.