title: Append 2D array to 3D array, extending third dimension
body: <p>I have an array <code>A</code> that has shape <code>(480, 640, 3)</code>, and an array <code>B</code> with shape <code>(480, 640)</code>.</p>
  
  <p>How can I append these two as one array with shape <code>(480, 640, 4)</code>? </p>
  
  <p>I tried <code>np.append(A,B)</code> but it doesn't keep the dimension, while the <code>axis</code> option causes the <code>ValueError: all the input arrays must have same number of dimensions</code>.</p>