FR: Improve key/value adding support to StringPairArray

The use-case is sorting out headers for networking purposes. In a bunch of circumstances it would really help to be able to do something like the following, considering the URL APIs are based around StringPairArray:

url.withParameters({
            { "key1", "value1 },
            { "key2", "value2" },
            { "key3", "value3" }
        });