Add rules between parameters

[rodber]

The library at this time doesn't have a process for comparing rules between parameters. For example, it can accept date_from and date_to parameters, but it doesn't have a mechanism for determining that date_to must be greater than date_from or any other conditional.

#[Restrictions(
    date_to: 'greater_than=date_from'
)]

I hate the syntax, needs work but the general idea is to provide an attribute where you can define applicable rules between argument values.