Quaternion: refactor multiplication to matrix multiplication style

Most often the multiplication in convention descriptions and papers is
described in matrix multiplication style like this:
q · p := Q(q)p

Q(q) :=
[q0 −q1 −q2 −q3]
[q1 q0 −q3 q2]
[q2 q3 q0 −q1]
[q3 −q2 q1 q0]

I'm just rearanging the terms such that it's easily comparable with
these definitions additional to it being clearly described by
documenting we use the hamilton convention.

matrix/Quaternion.hpp

@@ -252,14 +252,14 @@ public:
      * @param q quaternion to multiply with
      * @return product
      */
-    Quaternion operator*(const Quaternion &q) const
+    Quaternion operator*(const Quaternion &p) const
     {
-        const Quaternion &p = *this;
+        const Quaternion &q = *this;
         return {
-            p(0) * q(0) - p(1) * q(1) - p(2) * q(2) - p(3) * q(3),
-            p(0) * q(1) + p(1) * q(0) + p(2) * q(3) - p(3) * q(2),
-            p(0) * q(2) - p(1) * q(3) + p(2) * q(0) + p(3) * q(1),
-            p(0) * q(3) + p(1) * q(2) - p(2) * q(1) + p(3) * q(0)};
+            q(0) * p(0) - q(1) * p(1) - q(2) * p(2) - q(3) * p(3),
+            q(1) * p(0) + q(0) * p(1) - q(3) * p(2) + q(2) * p(3),
+            q(2) * p(0) + q(3) * p(1) + q(0) * p(2) - q(1) * p(3),
+            q(3) * p(0) - q(2) * p(1) + q(1) * p(2) + q(0) * p(3) };
     }
 
     /**