ERC20 Implmentation

• Fully functional ERC20 (includes eip-2612) written in Huff (based on Solmate).
• Passes all Solmate tests (except for invariant tests -- DappTools not supported in this repo).
• Includes transferFrom() and permit() functions, which are not included in any currently available implementations that I've seen.
• Because there's no immutables in Huff, meta data that is available in advance (name, symbol, decimals) is hardcoded into the fns. ChainID and INITIAL_DOMAIN_SEPARATOR use storage.

TODO:

• [ ] add missing revert strings
• [ ] refactor / gas golf -- TransferFrom especially needs some tlc