xapian-bridge C port

endlessm/eos-sdk#2463
That's not correct... The original code re-wrapped the query options as received by `libsoup` in `xapianBridge.js` and while it did so, it changed `query.collapse` to `options.collapse_key`. Instead, now I'm passing the query options hash table directly from `libsoup`, so I need to use the original name.