Demo update

-added 'dot' function to vector math
-fixed Circle tool rendering
-fixed some potentiall memory leaks
-added 'collision' module which now separates ShootGrid from SpaceInvaders demo
-separate some systems from demos to 'basic' module to better demos functionality sharing
-slow down snake
-added new graphics
-BrickBreaker demo now works (without blocks breaking and with bugged collision detection)

-some bug fixes

demos/utils/source/ecs_utils/math/vector.d

@@ -95,6 +95,11 @@ struct vec2
     }
 }
 
+float dot(vec2 a, vec2 b)
+{
+    return a.x*b.x + a.y*b.y;
+}
+
 struct vec4
 {
     union