title: argmax on 2 axis for 3-d numpy array
body: <p>I'd like to obtain a 1D array of indexes from a 3D matrix.</p>
  
  <p>For instance given <code>x = np.random.randint(10, size=(10,3,3))</code>, I'd like to do something like <code>np.argmax(x, axis=(1,2))</code> just like you can do with <code>np.max</code>, that is, obtain a 1D array of length 10 containing the indexes (0 to 8) of the maximums of each submatrix of size <code>(3,3)</code>.</p>
  
  <p>I have not found anything helpful so far and I want to avoid looping on the first dimension (and use <code>np.argmax(x)</code>) as it is quite big.</p>
  
  <p>Cheers!</p>