* Made string_span details::string_length() generic
removed overloads & specialized classes
Creating string_spans using `char16_t` and `char32_t` was not possible
without creating new specializations and function overloads.
This patch makes details::string_length() generic removing the need to
extend the overloads and specializations.
* added type aliases for string_span types char16_t and char32_t
* Added char16_t & char32_t overloads for ensure_z
* added string_span tests for char16_T & char32_t
* added zstring type aliases for char16_t & char32_t
* Added tests for char16_t & char31_t zstring and string_span types
* applies clang format to <gsl/string_span>
* Clang format tests/string_span_tests.cpp
* Removed ensure_z() overloads as they don't add functionality.
Project files were not following the clang-format style. For people
using IDEs were clang-format is always run after a save this would
cause unwanted changes.
This commit only applies "clang-format -i" to files.
* Improve const correctness in string_span
* Improve const correctness in bounds_tests.cpp and byte_tests.cpp
* Improve const correctness in span_tests.cpp
* Improve const correctness in utils_tests.cpp
* Use gsl::owner for dynamically allocated memory in string_span_tests.cpp
* Improve const correctness in string_span_tests.cpp
* Improve const correctness for strided_span_tests.cpp
* Nest "gsl" directory inside a new "include" directory.
* Cleanup the _MSC_VER conditionals a bit; use constexpr on VS2017+.
* Don't #define noexcept on non-Microsoft implementations.
* Workaround VS2017 bug in multi_span. (Also implement == and != for static_bounds_dynamic_range_t because I'm an EoP semantic soundness snob.)
Fixes#441.
