Except otherwise noted, all flags are by Hampus Nilsson. 
They are public domain, under the SAX-PD notice.
https://hampusborgos.github.io/country-flags/
https://github.com/hampusborgos/country-flags
https://github.com/hjnilsson/country-flags

The flag of the Arab League is public domain, uploaded by Flad 
to Wikimedia Commons.

In the bare repository the flags are missing. On GNU/Linux, use
the fetchflags.sh to fetch them.
