Add support for ERC1155/ERC721

[Arinerron]

Add a tokenId field to the nullifier.

• For ERC20, tokenId would always be 0
• For ERC721, amount would always be 1
• For ERC1155, both fields would be used

Split would not allow an ERC721 (amount of 1) to be split fractionally of course.

Question: how can the Solidity distinguish between ERC20 and ERC1155/ERC721 interfaces without a type field?

NOTE: technically if we wanted only ERC20 and ERC721 we could use the token field for everything.

[Arinerron]

I think it's simpler than this. See this file:

https://github.com/Zellic/zkerc20/blob/main/contracts/extensions/ERC721Node.sol#L8-L20