How to use the custom light position evaluator:
 * Init code will be executed each time the window size is changed
   or when the effect loads
 * Frame code is executed before rendering a new frame
 * Beat code is executed when a beat is detected

Predefined variables:
 x : Light x position, ranges from 0 (left) to 1 (right) (0.5 = center)
 y : Light y position, ranges from 0 (top) to 1 (bottom) (0.5 = center)
 isBeat : 1 if no beat, -1 if beat (weird, but old)
 isLBeat: same as isBeat but persists according to 'shorter/longer' settings
          (usable only with OnBeat checked)
 bi:	Bump intensity, ranges	from 0 (flat) to 1 (max specified bump, default)
 You may also use temporary variables accross code segments

Some examples:
   Circular move
      Init : t=0
      Frame: x=0.5+cos(t)*0.3; y=0.5+sin(t)*0.3; t=t+0.1;
   Nice motion:
      Init : t=0;u=0
      Frame: x=0.5+cos(t)*0.3; y=0.5+cos(u)*0.3; t=t+0.1; u=u+0.012;