generate-cmdlist.sh: do not shell out to "sed"
Replace the "sed" invocation in get_synopsis() with a pure-shell
version. This speeds up generate-cmdlist.sh significantly. Compared to
HEAD~ (old) and "master" we are, according to hyperfine(1):
'sh generate-cmdlist.sh command-list.txt' ran
12.69 ± 5.01 times faster than 'sh generate-cmdlist.sh.old command-list.txt'
18.34 ± 3.03 times faster than 'sh generate-cmdlist.sh.master command-list.txt'
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>