Expose removal of keys (HTTP params) from query

Hi Mario, another pull request for your consideration.

I've added an optional second parameter to the _normalize_ method, which itself has an optional _removeKeys_ key. If set, this can be used to remove keys from the query.

This change maintains backwards compatibility by continuing to remove _phpsessid_ and _utm*_ Google Analytics keys, with the latter becoming an explicit list rather than a "starts with" check.