Allow more than one Request param with the same key.

Many services allow a param to be added to a request multiple times, ie:

https://www.myfakeservice.com/this/is/a/test?param=fakeparam&param=anotherfakeparam/

There was no way that I could decipher in the original code to do this so I added new put methods to take a key and an ArrayList of Strings for the values. Now all you would need to do is something like this:

RequestParams params = new RequestParams();
ArrayList<String> dupParam = new ArrayList<String>();
            dupParam.add("ONE");
            dupParam.add("TWO");
            params.put("numbers", dupParam);