Changes

• Enhancement #104, on POSIX backend: optimized reuse of status information and reduced directory_entry creation leads to about 20%-25% in tests with recursive_directory_iterator over a larger directory tree.
• Pull request #103, wchar_t was not in the list of supported char types on non-Windows backends.
• Pull request #102, improved string_view support makes use of <string_view> or <experiemental/string_view> when available, and allows use of custom basic_string_view implementation when defining GHC_HAS_CUSTOM_STRING_VIEW and importing the string view into the ghc::filesystem namespace before including filesystem header.
• Pull request #101, fix for #100, append and concat type of operations on path called redundant conversions.
• Pull request #98, on older linux variants (GCC 7/8), the comerative std::filesystem tests now link with -lrt to avoid issues.
• Fix for #97, on BTRFS the test case for fs::hard_link_count failed due to the filesystems behavior, the test case was adapted to take that into account.
• Pull request #96, the export attribute defines GHC_FS_API and GHC_FS_API_CLASS are now honored when when set from outside to allow override of behavior.
• Fix for #95, the syntax for disabling the deprecated warning in tests in MSVC was wrong.
• Pull request #93, now the CMake configuration file is configured and part of the make install files.