implement accessibility support in archiso

this fixes #67
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failed lint #7570

00:00:30

 
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failed
lint Build

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num_usable_cards=$(nwords "$usable_cards")

For more information:
https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...
https://www.shellcheck.net/wiki/SC2003 -- expr is antiquated. Consider rewr...
make: *** [Makefile:22: lint] Error 1
ERROR: Job failed: exit code 1