[name]
		Implementation of a 
quaternion. This is used for rotating things without encountering the dreaded 
gimbal lock issue, amongst other advantages.
Example
		var quaternion = new THREE.Quaternion();
		quaternion.setFromAxisAngle( new THREE.Vector3( 0, 1, 0 ), Math.PI / 2 );
		var vector = new THREE.Vector3( 1, 0, 0 );
		vector.applyQuaternion( quaternion );
		
		Constructor
		[name]( [page:Float x], [page:Float y], [page:Float z], [page:Float w] )
		
		x - x coordinate
		y - y coordinate
		z - z coordinate
		w - w coordinate
		
		Properties
		[property:Float x]
		[property:Float y]
		[property:Float z]
		[property:Float w]
		Methods
		[method:Quaternion set]( [page:Float x], [page:Float y], [page:Float z], [page:Float w] )
		
		Sets values of this quaternion.
		
		[method:Quaternion copy]( [page:Quaternion q] )
		
		Copies values of *q* to this quaternion.
		
		[method:Quaternion setFromEuler]( [page:Euler euler] )
		
		Sets this quaternion from rotation specified by Euler angle.
		
		[method:Quaternion setFromAxisAngle]( [page:Vector3 axis], [page:Float angle] )
		
		Sets this quaternion from rotation specified by axis and angle.
		Adapted from [link:http://www.euclideanspace.com/maths/geometry/rotations/conversions/angleToQuaternion/index.htm].
		*Axis* is asumed to be normalized, *angle* is in radians.
		
		[method:Quaternion setFromRotationMatrix]( [page:Matrix4 m] )
		
		Sets this quaternion from rotation component of *m*.
		Adapted from [link:http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/index.htm].
		
		[method:Quaternion setFromUnitVectors]( [page:Vector3 vFrom], [page:Vector3 vTo] )
		
		Sets this quaternion to the rotation required to rotate direction vector *vFrom* to direction vector *vTo*.
		Adapted from [link:http://lolengine.net/blog/2013/09/18/beautiful-maths-quaternion-from-vectors].
		*vFrom* and *vTo* are assumed to be normalized.
		
		[method:Quaternion inverse]()
		
		Inverts this quaternion.
		
		[method:Float length]()
		
		Computes length of this quaternion.
		
		[method:Quaternion normalize]()
		
		Normalizes this quaternion.
		
		[method:Quaternion multiply]( [page:Quaternion b] )
		
		Multiplies this quaternion by *b*.
		
		[method:Quaternion multiplyQuaternions]( [page:Quaternion a], [page:Quaternion b] )
		
		Sets this quaternion to *a x b*
		Adapted from [link:http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/quaternions/code/index.htm].
		
		[method:Quaternion multiplyVector3]( [page:Vector3 vector], [page:Vector3 dest] )
		
		Rotates *vector* by this quaternion into *dest*.
		If *dest* is not specified, result goes to *vec*.
		
		[method:Quaternion clone]()
		
		Clones this quaternion.
		
		[method:Array toArray]( [page:Array array] )
		
		array -- Array to store the quaternion.
		
		
		Returns the numerical elements of this quaternion in an array of format (x, y, z, w).
		
		[method:Boolean equals]([page:Quaternion v])
		
		v -- Quaternion that this quaternion will be compared to.
		
		
		Compares each component of *v* to each component of this quaternion to determine if they
		represent the same rotation.
		
		[method:Float lengthSq]()
		
		Calculates the squared length of the quaternion.
		
		[method:Quaternion fromArray]([page:Array array])
		
		array -- Array of format (x, y, z, w) used to construct the quaternion.
		
		
		Sets this quaternion's component values from an array.
		
		[method:Quaternion conjugate]()
		
		Returns the rotational conjugate of this quaternion. The conjugate of a quaternion
		represents the same rotation in the opposite direction about the rotational axis.
		
		[method:Quaternion slerp]([page:Quaternion quaternionB], [page:float t])
		
		quaternionB -- The other quaternion rotation
		t -- Normalized 0 to 1 interpolation factor
		
		
		Handles the spherical linear interpolation between quaternions. *t* represents the amount of rotation
		between this quaternion (where *t* is 0) and quaternionB (where *t* is 1). This quaternion is set to
		the result. Also see the static version of the *slerp* below.
		
		
		// rotate a mesh towards a target quaternion
		mesh.quaternion.slerp( endQuaternion, 0.01 );
		
		
		
		Static Methods
		[method:Quaternion slerp]( [page:Quaternion qStart], [page:Quaternion qEnd], [page:Quaternion qTarget], [page:Float t] )
		
		qStart -- The starting quaternion (where *t* is 0)
		qEnd -- The ending quaternion (where *t* is 1)
		qTarget -- The target quaternion that gets set with the result
		t -- Normalized 0 to 1 interpolation factor
		
		
		Unlike the normal method, the static version of slerp sets a target quaternion to the result of the slerp operation.
		
		
		// Code setup
		var startQuaternion = new THREE.Quaternion().set( 0, 0, 0, 1 ).normalize();
		var endQuaternion = new THREE.Quaternion().set( 1, 1, 1, 1 ).normalize();
		var t = 0;
		
		
		// Update a mesh's rotation in the loop
		t = ( t + 0.01 ) % 1; // constant angular momentum
		THREE.Quaternion.slerp( startQuaternion, endQuaternion, mesh.quaternion, t );
		
		
		
		Source
		[link:https://github.com/mrdoob/three.js/blob/master/src/[path].js src/[path].js]