New function reduce2scalar_seasonal_zonal, which averages over everything - but restricted
to the specified season and zone (latitude range).
Also an obsolete function is deleted, and a couple of typo fixes.
Keep separate track of which files went into the filetable (you could just pull that out of the
rows one-by-one).  This isn't necessary for anything, but is a minor convenience in debugging.
Import amwg1, the code for plot set 1.
New file amwg1.py has the code for AMWG plot set 1.  I put it in a separate file
because it is fundamentally different from the rest - a text table, no plots.
Support AMWG plot set 1, and potentially other plot sets which are really text tables.