Format: SHOW PROMPT prompt-type

 Where prompt-type is one of: LINE, KEYPAD, NOKEYPAD, HCCHANGE, INSERT,
 INSERTN, or QUERY.

 The SHOW PROMPT command shows the current string to be used when
 prompting in line mode, in keypad change mode, in nokeypad change mode,
 in hardcopy change mode, in line mode when inserting, in line mode when
 inserting with NONUMBERS, and in response to /QUERY, respectively.