Add filtered queries.

[jpountz]

This is an alternative to #63 that adds filtered queries instead of new filtering commands.

Queries support optional filtering via the following syntax: " WHERE ", so engines can split on " WHERE " and interpret the left part as a required clause that computes scores and the right part as a filter. Only the Lucene 10 engines support this for now.

[PSeitz]

Thanks for the PR. I think we could make the handling slightly simpler when we move the WHERE clause to and extra "filter" field next to "query". What do you think?

[jpountz]

Can you explain a bit more what you have in mind? It was convenient to avoid introducing a third column in the protocol that src/client.py uses to submit queries to engines, or in the results web page. And then I kept the queries.txt file the same for consistency.

[PSeitz]

Can you explain a bit more what you have in mind? It was convenient to avoid introducing a third column in the protocol that src/client.py uses to submit queries to engines, or in the results web page. And then I kept the queries.txt file the same for consistency.

I was thinking the API with a third "filter" parameter would be a little bit clearer. For the results we could still have a single column with query + "WHERE " + filter

[jpountz]

@PSeitz I looked into your suggestion, but having different formats in the queries.txt and the results file while doing the conversion in src/client.py looks a bit awkward. It's possible that I misunderstood your suggestion, if so I'd appreciate if you could describe how you expect queries to look like in queries.txt, results.json and in the protocol that is used between src/client.py and the engines.