Created by: chorman0773
Implements <span> from C++2a. This header provides std::span and all associated features in <span> as described by https://en.cppreference.com/w/cpp/header/span. The Pull Request is intended to add these to libstd++ which is currently not provided by GCC. This header comes with the guarentee that it follows the specification described in the above resource. It is not guarenteed to be Complient with the latest version of the C++2a standard working draft, or any later version, should the header and/or class specification change.