Drop having a separate type for style options and make them all strings,

which allows formats to be expanded. Any styles without a '#{' are still
validated when they are set but any with a '#{' are not. Formats are not
expanded usefully in many cases yet, that will be changed later.

To make this work, a few other changes:

- set-option -a with a style option automatically appends a ",".

- OSC 10 and 11 don't set the window-style option anymore, instead the
  fg and bg are stored in the pane struct and act as the defaults that
  can be overridden by window-style.

- status-fg and -bg now override status-style instead of trying to keep
  them in sync.

cmd-respawn-pane.c

@@ -90,6 +90,7 @@ cmd_respawn_pane_exec(struct cmd *self, struct cmdq_item *item)
 	}
 
 	wp->flags |= PANE_REDRAW;
+	server_redraw_window_borders(wp->window);
 	server_status_window(wp->window);
 
 	environ_free(sc.environ);