Allow Cmp to big.Int without converting big.Int

[wjmelements]

Feature

func (*uint256.Int) CmpBig(big.Int) int

Motivation

Generally uint256.Int is superior and should replace big.Int everywhere. But in forked or in sufficiently large codebases it may not be practical or necessary to replace all instances. At the boundaries, this function could circumvent an explicit conversion.

I didn't find this feature when I looked for it so please close this if it already exists.