title: how to convert a matrix in dlib to a std::vector
body: <p>I have a colume vector defined in dlib. How can I convert it to std::vector?</p>
  
  <pre><code>typedef dlib::matrix&lt;double,0,1&gt; column_vector;
  column_vector starting_point(4);
  starting_point = 1,2,3,4;
  std::vector x = ??
  </code></pre>
  
  <p>Thanks</p>