Before this patch we were supporting only boolean option flags - with, for
example, stats[rf] meaning stats query with {"rf": True} arguments. Now we add
support for arbitrary types, so that it is possible to specify e.g. integer or
string query options, as well as some boolean flag set to false.

This should be good for generality.

For backward compatibility the old way to implicitly specify "on" flags is
continued to be supported.