Implement ERC721A

[iam4x]

The goal of ERC721A is to provide a fully compliant implementation of IERC721 with significant gas savings for minting multiple NFTs in a single transaction. This project and implementation will be updated regularly and will continue to stay up to date with best practices.

https://github.com/chiru-labs/ERC721A

What do you think?

[dabbott]

The concept of ERC721A is great! I think it would be a great option to have and I'd definitely accept a PR for it.

Much like the "reduced deployment costs option", this has tradeoffs in costs/complexity from the OpenZeppelin implementation, so I probably would make it opt-in rather than the default