Support solidity overloaded methods

[Lohann]

Issue

Solidity supports method overloading and Rust don’t.

How to Reproduce

Currently ethabi-derive and ethabi-contract doesn't support contracts with overloaded methods, like the ERC721 standard:

function safeTransferFrom(address from, address to, uint256 tokenId) external;
function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;

if you attempt to use

use_contract!(erc721, "../res/ERC721.abi")

Rust will complain with following error:

   | use_contract!(erc721, "../res/ERC721.abi");
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   | |
   | `safe_transfer_from` redefined here
   | previous definition of the module `safe_transfer_from` here
   |
   = note: `safe_transfer_from` must be defined only once in the type namespace of this module
   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

Proposal

For ethabi-derive, I included a new attribute ethabi_function_options, which receives function parameters.

pub mod erc721 {
    #[derive(ethabi_derive::EthabiContract)]
    #[ethabi_contract_options(path = "../res/ERC721.abi")]
    #[ethabi_function_options(
        signature = "safeTransferFrom(address,address,uint256,bytes)",
        alias = "safe_transfer_from_with_data"
    )]
    struct _Dummy;
}

For ethabi-contract, I included a new Macro Rule which accepts custom function options.

use_contract!{
    erc721,
    "../res/ERC721.abi"
    "safeTransferFrom(address,address,uint256,bytes)" => "safe_transfer_from_with_data",
    "safeTransferFrom(address,address,uint256)" => "regular_safe_transfer_from",
}

erc721::functions::safe_transfer_from_with_data::encode_input(...);
erc721::functions::regular_safe_transfer_from::encode_input(...);