add new configuration switch NORST

- will be needed for contests which do not record any exchange (e.g.
  ARRLFD or CW Open)
do not add RST into log if NORST is set

- just add '---' instead
do not show RST if NORST is set

- just display '---' instead
suppress redisplay of RST after PgUp/PgDwn if NORST is set

- It does not make sense to change RST if no RST is used.
add missing external definition
Rename keyword to 'NO_RST'
document NO_RST in man page and add it to arrlfd rule file
Merge branch 'no_RST'