SG-721

SG-721 is a cw721-compatible spec that adds on-chain contract metadata, including royalties.

```rs pub struct CollectionInfo { pub creator: String, pub description: String, pub image: String, pub externallink: Option, pub tradingstarttime: Option, pub royaltyinfo: Option, }

pub struct RoyaltyInfo { pub payment_address: Addr, pub share: Decimal, }

```

The above is set when the contract is instantiated. The contract inherits everything else from cw721-base.