An 3D arrow object for visualizing directions.
		var dir = new THREE.Vector3( 1, 2, 0 );
		//normalize the direction vector (convert to vector of length 1)
		dir.normalize();
		var origin = new THREE.Vector3( 0, 0, 0 );
		var length = 1;
		var hex = 0xffff00;
		var arrowHelper = new THREE.ArrowHelper( dir, origin, length, hex );
		scene.add( arrowHelper );
		
		
		[page:Vector3 dir] -- direction from origin. Must be a unit vector. 
		[page:Vector3 origin] -- Point at which the arrow starts.
		[page:Number length] -- length of the arrow. Default is *1*.
		[page:Number hex] -- hexadecimal value to define color. Default is 0xffff00.
		[page:Number headLength] -- The length of the head of the arrow. Default is 0.2 * length.
		[page:Number headWidth] -- The length of the width of the arrow. Default is 0.2 * headLength.
		
See the base [page:Object3D] class for common properties.
Contains the line part of the arrowHelper.
Contains the cone part of the arrowHelper.
See the base [page:Object3D] class for common methods.
		color -- The desired color.
		Sets the color of the arrowHelper.
		
		length -- The desired length.
		headLength -- The length of the head of the arrow.
		headWidth -- The length of the width of the arrow.
		Sets the length of the arrowhelper.
		
		dir -- The desired direction. Must be a unit vector.
		Sets the direction of the arrowhelper.
		
[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]