[boost] Automatically updating libs/maintainers.txt

Hi, I've just written a little script to update libs/maintainers.txt from the library metadata. You can see the main changes here: https://github.com/boostorg/boost/commit/94897806350320ac87d629bb933d5aea4d7... I've only done this on develop so far, so nothing's final. I will do the library list as well soon, but that might be a bit more disruptive. Daniel