Add initial prototype.

3-mid/physics/interface/source/physics-shape.ads

@@ -0,0 +1,17 @@
+package physics.Shape
+--
+-- Models a physical shape.
+--
+is
+   type Item is limited interface;
+   type View is access all Item'Class;
+
+   procedure define (Self : in out Item) is abstract;
+
+   procedure free     (Self : in out View);
+
+   procedure Scale_is (Self : in out Item;   Now : in math.Vector_3) is abstract;
+   procedure evolve   (Self : in out Item;   By  : in Duration)      is null;
+   procedure destruct (Self : in out Item)                           is abstract;
+
+end physics.Shape;