Fix set utc week 53

Hello. Thanks for the library. Came across an edge case in `setUTCWeek`. If we're on 2009-W53-07 (Sun 3 Jan 2010) and we call `getUTCWeek()` we get 53, as we should.

However, if we then call `setUTCWeek(53)` we'll get a totally different date back - Mon, 03 Jan 2011 00:00:00 GMT.

I changed `setUTCWeek` to use a new function `getUTCWeekNumberingYear()` ([nomenclature source](http://en.wikipedia.org/wiki/ISO_8601#Week_dates)) which'll return 2009 for UTC(2010,1,3). This then gets us to 2009-W53-01 as the documentation states.

There's 2 commits in the PR - the first that fails, the second that passes with the new code.