Merge: nitcorn: decode GET args from percent encoding

While POST data was decoded from percent encoding, GET args were not. Some clients (`shibuqam`) manually decoded that args while others (`benitlux`) hung on requests with spaces.

There is still an issue in the HTTP request parsing where request URL with a space are broken. I'm not fixing this right away because there is no current issue associated to this problem and I have a larger rewrite of nitcorn in the works that will solve this.

Pull-Request: #2322