title: Invert 0 and 1 in a binary array
body: <p>Is there a function in Numpy to invert 0 and 1 in a binary array?
  If</p>
  
  <pre><code>a = np.array([0, 1, 0, 1, 1])
  </code></pre>
  
  <p>I would like to get:</p>
  
  <pre><code>b = [1, 0, 1, 0, 0]
  </code></pre>
  
  <p>I use:</p>
  
  <pre><code>b[a==0] = 1
  b[a==1] = 0
  </code></pre>
  
  <p>but maybe it already exist something in Numpy to do this.</p>