Gnssrefl

Improvements:

* Added ediff as commandline input to quickLook. The default is 2 degrees and is meant as a
quality control parameters. If you choose 5 and 20 degrees as your elevation angle limits, this
would mean your arcs should be at least from 7 to 18 degrees. If you want to
allow shorter arcs than this, you can make ediff much larger. Within gnssir, it can be defined
in the json file.

New Features:

* refl_zones module added. Command line driven.

* EGM96 is now accessible from gps.py. This provides simple geoid corrections in meters
as a function of latitude and longitude.

Improvements:

* updated download_ioc to allow multi month downloads.

Bug fixes:

* fixed bug in invsnr that did not allow SNR files unless they were uncompressed.
Code now allows xz and gz compression

New Features:

* Changed how CDDIS archive is used, from a wget subprocess call to using FTPS.
This required checking that downloaded file was not zero size.

New Features:

* [Soil moisture module added](https://github.com/kristinemlarson/gnssrefl/blob/master/docs/pages/README_vwc.md)
vwc_input and vwc are the main programs.