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/source/gui/tool_circle.d

@@ -26,6 +26,7 @@ struct ToolCircle
 
     void draw(Renderer* renderer, vec2 position, float size, float edge = 1)
     {
+        glDisable(GL_DEPTH_TEST);
         position = position * renderer.view_size + renderer.view_pos;
         vec2 sizes = renderer.view_size * size;
         vec2 sizes2 = vec2(edge,0);