Updated data, Add rough average # of sats, add support for N threads and N degrees with wrapper script

[N6UDP]

This includes @c2h5oh's changes in #21 with some additional changes. Unfortunately due to the line ending changes in c2h5oh's changes I based this off of Github's diff/compare tool makes main.py's changes hard to look at - I recommend using an offline diff tool to avoid looking at the whitespace only changes.

https://n6udp.github.io/starlink-coverage/ has the live version.

Additional changes:

• Updated data as of 5/7/2021 with note (#20 - this should probably be automatic), added 30 degree data
• Added rough satellites overhead average
• gen_cov.sh, main.py, merge_cover.py updated to support an arbitrary number of threads (#9 partial)
• gen_cov.sh updated to generate multiple degrees in one run and to rename and move files as needed (addresses #9 to an extent)
• Dependencies at least partially documented
• commented out broken exclude list of sats adding some other exclusion criteria (related slightly to #18 as are @c2h5oh's changes to whitespace)
• gitignore