Expose queries API

[mwilliammyers]

I think we should expose the queries sub crate; many thanks to @stephanbuys for the awesome crate!

TODO:

• [ ] Integrate it into the main elastic crate or keep it as a sub-crate?
• [ ] Relation to rs-es?
• [ ] Keep derive_builder dependency?
  • [ ] Update derive_builder
• [ ] Remove error-chain dependency?
• [ ] Improve docs
• [ ] Make all enum fields UpperCamelCase
• [ ] Add more fields to the Query struct
• [ ] Add more aggregations
• [ ] Flesh out Bool struct (improve bool filter support)
  • [ ] Add minimum_should_match, boosting etc.
  • [ ] Make it so bool filters can be nested