forked from microsoft/GSL
* deprecated features adopted into C++ 1) Mark the following GSL features as deprecated: - gsl::unique_ptr (always) - gsl::shared_ptr (always) - gsl::byte (since c++17) - gsl::joining_thread (never implemented) 2) Refactor existing deprecations to use the new GSL_DEPRECATED(msg) macro. 3) Create a section in the README for deprecated features in the standard. * do not deprecate gsl::to_integer because we never claim to implement it. * do not use gsl::byte if it is deprecated