non-functional checks for std::string_view support #1334
Description
I noticed that in VS syntax highlighting was showing as if std::string_view isn't supported inside decimal, even though in my project I use latest c++ available:
decimal\decimal64_t.hpp
The reason is that __cplusplus shouldn't be used in VS to check for supported standard. They don't fully support something and for that reason they keep old/wrong version for __cplusplus. Instead, usually cpp feature test macro or _MSC_LANG should be tested.
decimal\detail\config.hpp:
