[boost] Switch library review extended to Sunday, Jan 13th

The review for the Switch library has been extended to Sunday, January 13th. I hope that the extended period will provide an opportunity for more reviewers to submit their vote, and give enough time for the discussion on design to resolve. As this library is both small and seen as very useful, it seems preferable to take advantage of the momentum of the ongoing discussion between very knowledgeable reviewers and a very knowledgeable author, and get this ironed out now. Stjepan