Refactor wins_launch_external()

Allow for passing an arbitrary number of arguments. This also allows us
to remove wins_launch_external2() and use wins_launch_external() at all
call sites instead.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/help.c

@@ -189,7 +189,8 @@ int display_help(const char *topic)
 	}
 
 	if (io_file_exists(path)) {
-		wins_launch_external(path, conf.pager);
+		const char *arg[] = { conf.pager, path, NULL };
+		wins_launch_external(arg);
 		return 1;
 	} else {
 		return 0;