vector: implement swap()

src/vector.hpp

@@ -108,6 +108,13 @@ public:
             return *this;
         }
 
+    void swap(Vector& other)
+        {
+            storage_.swap(other.storage_);
+            std::swap(data_, other.data_);
+            std::swap(size_, other.size_);
+        }
+
     Scalar *data() const
         {
             return data_;