[FEAT] Convert milch into an application oriented library

[realstealthninja]

Currently milch operates as a library that provides one class which does everything.

instead it should really be providing Base classes that could be overridden
i.e:

#include <milch/milch.hpp>

class myApp : public milch::Application {

   void Input(Event* event) {
       // handle events here
   }

   void Update() {
      // draw things here
   }

   void Init() {
      // initalize things here

      // in the future it could even intialize widgets
      Button myButton("text", shapes::point(20, 30));
      this.add_widget(myButton);
      
   }

}

int main() {

   myApp app;
   app.run();
}