'move this out of __init__ because non-separable axes don\'t use it'

def _init_axis(self):

    self.xaxis = maxis.XAxis(self)
    self.spines[u'bottom'].register_axis(self.xaxis)
    self.spines[u'top'].register_axis(self.xaxis)
    self.yaxis = maxis.YAxis(self)
    self.spines[u'left'].register_axis(self.yaxis)
    self.spines[u'right'].register_axis(self.yaxis)
    self._update_transScale()
