Support query expander in query() function

I wanted to use the following API:

  query("MATCH_COLUMNS", "QUERY", {"query_expander": "QueryExpanderTSV"})

But this change uses the following API:

  query("MATCH_COLUMNS", "QUERY", "QueryExpanderTSV")

Because object literal (`{"XXX": "YYY"}`) syntax isn't supported yet. :<

TODO: document