laravel Package development, how to deal with the many-to-many relationship between Model in a package and Model outside the package?
 for example: 
 for example, we are going to write an awesome Article Package,. This package mainly provides functions related to managing articles. 
 if someone else wants to write a blog site and use the Article function, you can use our package directly. 
 but in some projects that use our Article package, we want Article to establish a many-to-many relationship with the User in the project. How do we define many-to-many relationships under Package"s Article? 
 for Article, this Pakcage,User, this Model may not exist. 
