Develop to master

[scotthavens]

A lot has changed to the HRRR retrieval and access for both grib2 and netcdf options. New changes are:

• pip install the package
• HRRR ftp access remains unchanged
• HRRR https access using grequests
• removed pygrib in favor of xarray
• grib2nc converter that uses wgrib2
• downloading is streamlined from the University of Utah
• tests have been developed for the major functionality
• Dockerfile for downloading from NOMADS

[scotthavens]

There are a few new additions since this:

• chunking in grib2nc
• retrieval no longer uses grequests do to a conflict with SRMF #8