make lines reformattable

- completely removed the old textbuffer representation (
  https://github.com/shabble/irssi-docs/wiki/Notes-256-Colour#textbuffer-encoding
  )

- textbuffer-formats is an extra module, so if we unhook the signals it
  should go back to the "old way" of storing pre-rendered tex

- design uses cache, original formats and list of arguments

src/fe-text/lastlog.c

@@ -199,7 +199,7 @@ static void show_lastlog(const char *searchtext, GHashTable *optlist,
 		}
 
                 /* get the line text */
-		textbuffer_line2text(rec, fhandle == NULL, line);
+		textbuffer_line2text(WINDOW_GUI(window)->view->buffer, rec, fhandle == NULL, line);
 		if (!settings_get_bool("timestamps")) {
 			struct tm *tm = localtime(&rec->info.time);
                         char timestamp[10];