Solitidy ABI

Solidity ABI implementation in Rust.

This is still a work in progress: - [x] Type-safe encoding - [x] Runtime encoding - [x] Type-safe decoding - [x] Runtime decoding - [x] Parsing of Solidity ABI JSON output - [x] Type-safe encoding and decoding of Solidity ABI items - [x] Runtime encoding and decoding of Solidity ABI JSON items - [ ] Procedural macros for Solidity ABI item generation - [ ] Derive macro for Encode and Decode