[boost] cstring_view

Hi y'all, I've hacked together a cstring_view class and would like to ask if it could be included in boost.utility or boost.core. https://gist.github.com/klemens-morgenstern/fc02dab8b37fc77ac80efbca30f297cf The main motivation is to have a view that works with C-APIs. I also need the char_traits for dealing with odd char semantics for some system APIs. (e.g. environment keys on windows are char-insensitive but preserving).