Implement Matrix3x3 missing members and documentation

src/J3ML/LinearAlgebra/Matrix4x4.cpp

@@ -667,7 +667,7 @@ namespace J3ML::LinearAlgebra {
     {
         assert(!ContainsProjection());
 
-        // a) Transpose the top-left 3x3 part in-place to produce R^t.
+        // a) Transposed the top-left 3x3 part in-place to produce R^t.
         Swap(elems[0][1], elems[1][0]);
         Swap(elems[0][2], elems[2][0]);
         Swap(elems[1][2], elems[2][1]);