Ability to validate strings as numbers

[davidmoshal]

Is your feature request related to a problem? Please describe.

Ability to validate if a string is a number.
Additionally, if it is a number, ability to validate as a number.
eg: if it's positive, is less than or greater than x, etc.

Describe the solution you'd like

Assuming a system which receives parameters as strings via REST.
(which is actually all http requests, as string, and string arrays, are the only parameter type).

I'd like to be able to validate as follows:

validate(Employee::age).isNumber().isPositive()

Additional context

Add any other context or screenshots about the feature request here.