* Added c++17 test configurations for clang5.0 and clang6.0
* Fixed CppCoreCheck warnings in GSL and tests
- Added CMakeSettings.json for VS Open Folder configuration
- So we can easily run CppCoreCheck in VS
- Fixed CppCorecheck warnings where it made sense
- Suppressed the rest
- Some suppression does not work due to compiler/tool bugs,
so replaced by #pragma disable
- CppCoreCheck has noise, suppressed those with comments
- Catch produces many warnings, blanket-supressed them all
- Had to fix clang formatting to keep attributes in place
- clang-format does not support attributes, so I am using
- "CommentPragmas: '^ NO-FORMAT:'" to skip formatiting on them
- Removed GSL_NOEXCEPT macro, removed incorred noexcepts
* Ignore unknown attributes
* ignore unknown attributes in noexception mode tests
* fixed C26472 in at()
* created GSL_SUPPRESS macro to allow all compilers to parse suppression attributes
* try to fix gcc compilation problems with attributes
* ignore gsl::suppress for gcc
* move suppression to function level on return statements
clang5.0 and up does not allow attributes on return statemets in constexpr functions
* move suppression to function level on return statements
* use GSL_SUPPRESS in algorithm_tests
* Addressed PR comments
