This patch adds support for std::unique_ptr and
std::shared_ptr to the gsl::span
class instead of having to manually grab the pointer via
get().
For reference, this is part of the following issue:
https://github.com/Microsoft/GSL/issues/402
When turning on the following flags, several additional warnings
were generated, which have been cleaned up in this patch. The
flags included:
-Wextra
-Wpedantic
-Wconversion
-Wsign-conversion
-Wctor-dtor-privacy
-Wshadow
-Wnon-virtual-dtor
-Wold-style-cast
-Wcast-align
-Woverloaded-virtual
span being a view and not a container, the generic version of gsl::at is not valid any more for span.
This commits adds a specialization of gsl::at for span
