MINOR: http: add a new fetch "query" to extract the request's query string

MINOR: http: add a new fetch "query" to extract the request's query string

This fetch extracts the request's query string, which starts after the first
question mark. If no question mark is present, this fetch returns nothing. If
a question mark is present but nothing follows, it returns an empty string.
This means it's possible to easily know whether a query string is present
using the "found" matching method. This fetch is the completemnt of "path"
which stops before the question mark.