2.1

• Zap now requires Python 3.5 or later, and Astropy 2.0 or later.

• Compatibility with the NFM-AO mode.

• Ignore the notch filter region in the 'median' and 'fit' methods for the
  continuum filter (cftype).

• Change the default continuum filter method (cftype) to 'median' and
  remove the 'weight' method. The previous default method ('weight') has some
  problems with the treatment of spectra edges and with the notch filter edges
  for the AO modes, and is also introducing bumps in the red wavelengths.

• Add a command-line argument for nevals.

• Scipy 0.18.1 or later is required, because of SVD convergence issue with
  previous versions.

• Add a function to mask the cube edges (zap.mask_nan_edges): the spaxels
  at the edges of the cube may have a lot of NaNs in their spectra, so ZAP
  does not subtract the sky on these which leaves high residuals.