Add example to docs of custom rule comparing two supplied pieces of data?

[domhnallw]

Hi all:

Would it be possible to add an example of a custom rule to the README that shows how to compare two items of supplied data, in the same way as the already-defined equals and different rules do? Even something simple like a lessThan or greaterThan rule would be great to illustrate how that would work.

Thanks :)

[domhnallw]

While we're on the subject, being able to use two items of data to check another (such as a 'between' method to check if a supplied value is between two others) would be great too :)