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.

names.c

@@ -96,6 +96,7 @@ check_window_name(struct window *w)
 	if (strcmp(name, w->name) != 0) {
 		log_debug("@%u new name %s (was %s)", w->id, name, w->name);
 		window_set_name(w, name);
+		server_redraw_window_borders(w);
 		server_status_window(w);
 	} else
 		log_debug("@%u name not changed (still %s)", w->id, w->name);