title: use variables as key names when using numpy savez
body: <p>After loading an npz file, I like being able to access arrays with keys, e.g.:</p>
  
  <pre><code>KEY1  = "names"
  file  = np.load(npzFilename)
  data  = file[KEY1]
  </code></pre>
  
  <p>But you have to manually force this when you save, i.e.:</p>
  
  <pre><code>np.savez(npzFilename, names=names)
  </code></pre>
  
  <p>Is there anyway to set the NPZ dictionary key using a variable?  i.e. something like</p>
  
  <pre><code>np.savez(npzFilename, names, key=KEY1)
  </code></pre>