Changed scalar_normal_dist_op to class with user-defined moved ctor

include/libcmaes/eigenmvn.h

@@ -47,12 +47,30 @@
 namespace Eigen {
   namespace internal {
     template<typename Scalar>
-      struct scalar_normal_dist_op
+      class scalar_normal_dist_op
       {
+private:
+    void swap(scalar_normal_dist_op &other) {
+      std::swap(rng, other.rng);
+      std::swap(norm, other.norm);
+    }
+public:
 	static std::mt19937 rng;                        // The uniform pseudo-random algorithm
 	mutable std::normal_distribution<Scalar> norm; // gaussian combinator
 
 	EIGEN_EMPTY_STRUCT_CTOR(scalar_normal_dist_op)
+
+    scalar_normal_dist_op &operator=(scalar_normal_dist_op &&other) 
+    {
+        if (this != &other) {
+            swap(other);
+        }
+        return *this;
+    }
+
+    scalar_normal_dist_op(scalar_normal_dist_op &&other) {
+        *this = std::move(other);
+    }
 
 	template<typename Index>
 	inline const Scalar operator() (Index, Index = 0) const { return norm(rng); }