Adds the EngineHandler struct
Removes vulnerability where an attacker could send requests cookies with fake engine names and crash the server.
Merged RawSearchResult and SearchResult, as they were functionally identical.
Refactor aggregation function
Rename visiting_url to url, as they are always the same (see upstream engine scalping).
Refactor parsing function to be more readable.
BREAKING: renames `binding_ip_addr` to `binding_ip` and `redis_connection_url` to `redis_url`.
Renames a lot of internals as well, but they are to many to mention.
