[boost] [release] New libraries documentation + release notes

Hi, I'm starting to compile the release notes, so please add the info for your library. Easy way to do so is to click the pencil icon at the top right of the code at: https://github.com/boostorg/website/blob/master/feed/history/boost_1_61_0.qb... Or you can just email me if you don't like quickbook. Also, the documentation for the new libraries in this release is now building okay and I've added links to the release notes, so please can the relevant people take a look: http://www.boost.org/users/history/version_1_61_0.html thanks, Daniel