Decode from a application/x-www-form-urlencoded String into a rune Object.

let result = urlencoded::decode("a=1&b=2&c=3&c=4&key_without_value&=value_without_key");
let map = #{};
map["a"] = "1";
map["b"] = "2";
map["c"] = "4";
map["key_without_value"] = "";
map[""] = "value_without_key";
assert_eq!(result, map);