builtin-notes: Minor (mostly parse_options-related) fixes

builtin-notes: Minor (mostly parse_options-related) fixes

Use PARSE_OPT_NONEG to disallow --no-<option> for message, file,
reedit-message and reuse-message. for which --no-<option> does not make
sense.  This also simplifies the code in the option-handling callbacks.

Also, use strbuf_addch(... '\n') instead of strbuf_addstr(... "\n") in
couple of places.

Finally, improve the short-help by dividing the options into two
OPT_GROUPs.

Suggested-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Johan Herland <johan@herland.net>
Acked-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>