Implement math/big evaluate operations

[vivlis]

Hello,

I like this package, but I have problem with floating numbers as for data type float64 limitation, which for my case is rounding and unmarshaling from JSON.

Describe the solution you'd like
Would like to propose implementation math/big to standard evaluation (https://github.com/hyperjumptech/grule-rule-engine/blob/master/pkg/reflectmath.go).
it can be done with something similar like:
if left.Type().String() == "big.Float" && right.Type().String() == "big.Float" {
leftValue := left.Interface().(big.Float)
rightValue := right.Interface().(big.Float)
return reflect.ValueOf(leftValue.Cmp(&rightValue) == 1), nil
}

Describe alternatives you've considered
I've considered to create custom function with strings inputs, which will/is #working nicely, but I think above could be nice addition to package.