Add support for charts to ASCII driver. Bug #16364.

Add support for charts to ASCII driver.  Bug #16364.
Thanks to John Darrington for review.

* ascii.c (struct ascii_driver_ext): Add chart_type,
chart_file_name, chart_cnt members.
(ascii_open_driver): Initialize new members.
(static array option_tab): Add new options, reorganize slightly.
(handle_option): Handle new options.
(ascii_submit): New function.
(ascii_chart_initialise): Implement.
(ascii_chart_finalise): Implement.

* chart.c (chart_init_separate): New function.
(chart_finalise_separate): New function.

* dummy-chart.c (chart_init_separate): New function.
(chart_finalise_separate): New function.

* html.c (html_open_driver): Don't free chart_file_name.
(html_close_driver): Do free chart_file_name.
(handle_option): Only give an error for chart-files options that
don't contain "#".
(html_initialise_chart): Use new chart_init_separate.
(html_finalise_chart): Use new chart_finalise_separate.