implemented Week of Year
Squashed commit of the following:

commit ed4e4a5d5a4511e72d00c520f3df51bcfa46de7f
Author: Ingolf Wagner <palipalo9@googlemail.com>
Date:   Mon Mar 17 19:33:27 2014 +1100

    should work with 2.9 now

commit 8a4f5f3a7434be4f47b4ce29bc1d1d3137b8795f
Author: Ingolf Wagner <palipalo9@googlemail.com>
Date:   Mon Mar 17 19:18:42 2014 +1100

    moar tests

commit 902a3d3ae1d6353ad1fe8df96457a23d50f6ab78
Author: Ingolf Wagner <palipalo9@googlemail.com>
Date:   Mon Mar 17 18:48:41 2014 +1100

    most of the problems solved

commit bff18d233ad5ae763065078f5bbfe7b4518ed765
Author: Ingolf Wagner <palipalo9@googlemail.com>
Date:   Mon Mar 17 17:10:37 2014 +1100

    find that implicit bug