Support for numpy.datetime64
----------------------------

Matplotlib has supported `datetime.datetime` dates for a long time in
`matplotlib.dates`.  We
now support `numpy.datetime64` dates as well.  Anywhere that
`dateime.datetime` could be used, `numpy.datetime64` can be used.  eg::

  time = np.arange('2005-02-01', '2005-02-02', dtype='datetime64[h]')
  plt.plot(time)