Radius update with changes to address original PR and review comments (#620)

* Update isd_generate.py

add in PROJ like options for radius names ("-a", "-r", "--radius", "-b")

* Update isd_generate.py

updated required statement for --semimajor to catch if only --semiminor or -b is sent. Request that radius is sent in meters and updated some typos.

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Co-authored-by: Austin Sanders <arsanders@usgs.gov>