Change wording for BindingResolutionException's where middleware has not been registered, to be more clear

[randohinn]

What are the possible ways to achieve a BindingResolutionException from \Illuminate\Container\Container.php:807, and would it be possible to make the exception wording ' Target class [member] does not exist. ' a bit less ambigous? For example, adding in a "Did you forget to register your middleware?" or something along these lines? Just spent several minutes trying to figure out why I was seeing this...