Illuminate\Bus\Dispatcher option to customise how a command handler is found

[bambamboole]

Currently it is only possible to add a command => handler mapping by calling the Illuminate\Bus\Dispatcher::map().
We are using a common pattern , where we place a command handler always next to the command. E.g. App\Foo\BarCommand::class will be handled by App\Foo\BarCommandHandler::class.

To achieve here, that the Illuminate\Bus\Dispatcher finds the handler automatically, I have to override the whole class, since it is not customisable how this works.

My idea was, to add the option to configure a commandHandlerResolver callback, which is then called in the getCommandHandler method of Illuminate\Bus\Dispatcher.

Would you accept a PR to add this feature?