Unify operator "message" option type / interface

[loreanvictor]

Many operators respond to incoming requests with preset status / messages. These status / messages are not fed to operators in a unified manner, some operators do not accept one (timeout()), some operators accept them directly as parameters (reject()) and others get them as part of an options object (check()).

Further more, the current situation does not allow for custom messages per request, which limits applicability. I would propose moving to a unified API, and all operators also accepting functions (sync or async) that would generate the message based on packet. I suspect passing them as part of an options object in a unified manner would result in a more readable outcome.