Adds a search transformer

[hipsterjazzbo]

I wanted to add the ability to search with Laravel Scout, but there's not really a way to add custom transformers at the moment at run time, and custom queries were very very verbose.

This PR adds a transformer to search with Laravel Scout, which is automatically activated when the Eloquent model uses Laravel\Scout\Searchable, similar to SoftDeletes.

[cmizzi]

Hi !

I'm currently working to use pipeline in order to write custom arguments and transformers. You'll be able to write custom pipe to append some custom arguments and resolver. Also, a configuration will be set to register custom transformers (I don't really think about that at now...).

I'll implement all of that as soon as possible (it will be more prettier that now) :)

[cmizzi]

The PR #24 is merged into master. You can now use pipes to modify requests/responses.