Use chainlink oracle

[werg]

We want to create a contract satisfying this interface: https://github.com/marginswap/marginswap-core/blob/main/interfaces/IOracle.sol

In order to do so we need:

Call chainlink

write a function using this chainlink library: import "@chainlink/contracts/src/v0.6/interfaces/AggregatorV3Interface.sol";

Here's a very rough sketch

address oracleAddress = tokenOracles[tokenAddress];
AggregatorV3Interface oracle = AggregatorV3Interface(oracleAddress);
        (
            uint80 roundID,
            int256 tokenPrice,
            uint256 startedAt,
            uint256 timeStamp,
            uint80 answeredInRound
        ) = oracle.latestRoundData();

return inAmount * tokenPrice * PEG_EXPONENT / oracleExponent[tokenADdress] / tokenExponent[tokenAddress];

This function likely would be a view function, so could be used to implement both the required functions of the interface.

Store metadata

We need a way to tell the contract which oracle to ask for each token, this should be a onlyOwnerExec gated function in the contract. It should store things such as the oracleExponent and tokenExponent as well as the address of teh oracle contract. You can find links to oracle contracts here