ABI encoding is out of date

This library is using `ethereumjs-abi`, which does not support the newer ABI_V2 spec and has been deprecated as a result: https://github.com/ethereumjs/ethereumjs-abi/issues/86

ABI_V2 changed the way `bytes` and `string` params are encoded and I know from personal experience that `ethereumjs-abi` does not decode newer messages properly. I don't know if the encoding side will work or not, but I would suggest considering a move to `ethers` if this repo is still in development.

Start by locating the library's uses of ethereumjs-abi and its ABI encoding and decoding entry points. Check the ABI_V2 behavior for bytes and string parameters, then evaluate the suggested ethers migration. Done means newer ABI_V2 messages encode and decode correctly, with tests covering those parameter types.

Written by the indexing model from the issue text.