I changed the "GLOGAL OPTIONS" help heading to use title case, to
match clap's new help style.
I also removed our override of the help text for `-h, --help` because
the default text now includes "(use `-h` for a summary)" (and it's
harder override now).
Perhaps the most obvious difference to users will be the changed help
output
(https://epage.github.io/blog/2022/09/clap4/#polishing-help-output). It
no longer has color, and long lines are not wrapped. I suppose we
should wrap the text ourselves instead..