code: def ndist(data,Xs):
      
      sigma=np.sqrt(np.var(data))
      center=np.average(data)
      curve=mlab.normpdf(Xs,center,sigma)
      curve*=len(data)*HIST_RESOLUTION
      return curve
docs: given some data and a list of X posistions, return the normal
      distribution curve as a Y point at each of those Xs.