UMIP 30 -Add ELASTIC_STABLESPREAD/USDC as a price identifier (DEPRECIATED)

This price identifier has been deprecated. It is highly recommended that contract deployers do not use this identifier in its current state for new contracts. Price requests for this identifier from contracts created after 02/26/21 00:00 UTC will likely not be resolved correctly. Price requests from contracts created before this time will not be impacted.

The DVM should support price requests for the ELASTIC_STABLESPREAD/USDC price index, denominated in USDC. ELASTIC_STABLESPREAD/USDC is defined as: min(max(A - B + 1, 0), 2) , where A refers to an equally weighted basket of {ESD, FRAX, BAC}. B is an equally weighted basket of {USDC, USDT}. ESD is Empty Set Dollar, an algorithmic stablecoin on Ethereum with a dynamic supply model. FRAX is a fractional-algorithmic stablecoin on Ethereum that operates on a creative approach to maintaining a peg via a partially collateralized approach. BAC is Basis Cash, a dynamic supply stablecoin on Ethereum, essentially a version of what the original Basis project meant to be a few years ago. USDC is a centralized stablecoin issued by Circle and Coinbase. USDT is a non-transparent centralized stablecoin issued by Tether, currently the most used stablecoin on Ethereum.