This version of Alsvid has been rewritten for to use astropy rather
than pyfits and pywcs.


The command line 


sed -i '/import pyfits/c\import astropy.io.fits as pyfits' *


in Linux changed all import functions to to use this library. This retains the
"pyfits" prefix to commands so that most of the code remains unaltered and still
easily read.

As of 2018-03-17, astropy requires Python >3.5 and Alsvid is forced to retain 
this dependency. However Alsvid will run with older versions of Astropy already
installed.

A cautionary note with astropy installed by yourself, the distribution has
chosen to add excecutable scripts to /usr/local/bin.  While these names do not
overwrite Alsvid scripts, there are no warnings issued and they could overwwrite
yours.