adding type alias for Route #114

Decided not to change the other methods, so it is easier to grasp what is the parameter while auto completing, 

The other methods are:
```scala

def orElse(that: PartialFunction[(Method, Path), Service[Req, Rep]])

def apply[Req <: HttpRequest, Rep](r: PartialFunction[(Method, Path), Service[Req, Rep]])

```

Should I change both too?