ons return information about the entire history list or
individual list entries.

 -- Function: HIST_ENTRY ** history_list (void)
     Return a 'NULL' terminated array of 'HIST_ENTRY *' which is the
     current input history.  Element 0 of this list is the beginning of
     time.  If there is no history, return 'NULL'.

 -- Function: int where_history (void)
     Returns the offset of the current history element.

 -- Function: HIST_ENTRY * current_history (void)
     Return the history entry at the current position, as determined by
     'where_history()'.  If there is no entry there, return a 'NULL'
     pointer.

 -- Function: HIST_ENTRY * history_get (int offset)
     Return the history entry at position OFFSET.  The range of valid
     values of OFFSET starts at 'history_base' and ends at
     HISTORY_LENGTH - 1 (*note History Variables::).  If there is no
     entry there, or if OFFSET is outside the valid range, return a
     'NULL' pointer.

 -- Function: time_t history_get_time (HIST_ENTRY *entry)
     Return the time stamp associated with the history entry ENTRY.  If
     the timestamp is missing or invalid, return 0.

 -- Function: int history_total_bytes (void)
     Return the number of bytes that the primary history entries are
     using.  This function returns the sum of the lengths of all the
     lines in the history.