quaternion: add convenience quaternion-vector multiply

quaternion.hpp

@@ -75,6 +75,15 @@ namespace util {
     rotate (vector3<T>, quaternion<T>);
 
 
+    //-------------------------------------------------------------------------
+    template <typename T>
+    vector3<T>
+    operator* (quaternion<T> const q, vector3<T> const v)
+    {
+        return rotate (v, q);
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     template <typename T>
     constexpr