devel/tl-expected 1.3.1 OpenBSD

tl-expected is a single header implementation of `std::expected` with functional-style extensions.

std::expected is proposed as the preferred way to represent an object which will either have an expected value, or an unexpected value giving information about why something failed. Unfortunately, chaining together many computations which may fail can be verbose, as error-checking code will be mixed in with the actual programming logic. This implementation provides a number of utilities to make coding with expected cleaner.