Move entityclass::setenemy() to entclass::setenemy()

This moves the setenemy() function onto the entity object itself,
instead of having to give the indice of the entity in obj.entities. This
makes the code more object-oriented so later I can simply change all
'entities[k]' to 'entity.' in entityclass::createentity().

desktop_version/src/Ent.h

@@ -10,6 +10,8 @@ public:
 
     bool outside();
 
+    void setenemy(int t);
+
 public:
     //Fundamentals
     bool active, invis;