Rewrite help for command-line options.
Rewrite help for command-line options.

The re-write describes each option consistently in terms of “make the
program do FOO”, and uses the ‘metavar’ feature to reference option
arguments.

Signed-off-by: Steven Tobin <steventtobin (at) gmail.com>

amiryal/XKCD-password-generator,amiryal/XKCD-password-generator