( [string varname [, string newvalue]] )
If called with no parameters, this function returns an array of
values for all the setting readline uses. The elements will
be indexed by the following values: done, end, erase_empty_line,
library_version, line_buffer, mark, pending_input, point, prompt,
readline_name, and terminal_name.
If called with one parameter, the value of that setting is
returned. If called with two parameters, the setting will be
changed to the given value.