Add exception conditions

[sagikazarmark]

By the time the middleware is pushed to the stack the application might not be aware of some details which could serve as an exception. For example if the requested route is a login page to an admin panel the application should allow the request instead of showing the maintenance page. A similar condition can be a logged in administrator. These are runtime details, thus there should be a way to match against these conditions runtime.

[davedevelopment]

I'd be reluctant to grow this lib to cater for several specific conditions, but would be happy to accept patches that involve injecting a callable $grantAccessRegardless or something