Merge branch 'patch-13' of https://github.com/gero3/three.js into dev

docs/api/objects/ParticleSystem.html

@@ -40,11 +40,16 @@
 
 		<h3>.[page:boolean sortParticles]</h3>
 		<div>
-		todo
+		When set, then the particles should be depth sorted (from far to near), based on camera, in the renderer every frame. 
 		</div> 
 
 		<h2>Methods</h2>
 		
+		<h3>.clone()</h3>
+		<div>
+		This creates a clone of the particle system.
+		</div> 
+		
 		<h2>Source</h2>
 
 		[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]