add a getSpotPrice getter to usingtellor?

[tkernell]

Something like this. It would abstract away the generation of queryData/queryIds for this particular query type. But then we wouldn't want to add a getter for every query type.

function getSpotPrice(string calldata _asset, string calldata _currency, uint256 _disputeBufferTime) 
        public 
        view 
        returns(
            bool _ifRetrieve,
            bytes memory _value,
            uint256 _timestampRetrieved
        ) {
        bytes memory _queryData = abi.encode("SpotPrice", abi.encode(_asset, _currency));
        return getDataBefore(keccak256(_queryData), block.timestamp - _disputeBufferTime);
}