Insert text into the line at the current cursor position.
Function: intrl_delete_text (int start, int end)
Delete the text between start and end in the current line.
Function: char*rl_copy_text (int start, int end)
Return a copy of the text between start and end in
the current line.
Function: intrl_kill_text (int start, int end)
Copy the text between start and end in the current line
to the kill ring, appending or prepending to the last kill if the
last command was a kill command. The text is deleted.
If start is less than end,
the text is appended, otherwise prepended. If the last command was
not a kill, a new kill ring slot is used.