C++17 support?

[camio]

Would you accept quality PRs that add C++17 support to this library? I think there's a large use case for this as a polyfill in that environment.

[ednolan]

This ties in to the discussion we've been having on Discourse about whether we should even allow C++17 in the Beman project:

https://discourse.bemanproject.org/t/potential-policy-change-making-c-20-the-minimum-library-implementation/581