Investigate potential for a "conditional" on routes

[splashsky]

While I don't want to complicate the router more than necessary, having a concise way to add route "conditions" (e.g. a user being logged in) in the router might be handy.

I don't want to escalate to the level of Laravel's powerful Middleware, but a simple ->if(Auth::loggedIn()) type of method you can chain onto the Router::get() method is worth investigating.

Would also address steampixel#44.

[compilekaiten]

I was about to make an issue suggesting this.

It would be great to be able to check individual routes, or guard prefixes/groups.

I'm using this project for an API, and just ended up making a class to check for a header, that I call on every route.

[splashsky]

Since I'm revisiting this project I might as well start looking into this again. 😄