ghc::filesystem Release v1.5.10

Changes:

• Pull request #136, the Windows implementation used some unnecessary expensive shared pointer for resource management and these where replaced by a dedicated code.
• Fix for #132, pull request #135, fs::remove_all now just deletes symbolic links instead of following them.
• Pull request #133, fix for fs::space where a numerical overflow could happen in a multiplication.
• Replaced travis-ci.org with GitHub Workflow for the configurations: Ubuntu 20.04: GCC 9.3, Ubuntu 18.04: GCC 7.5, GCC 8.4, macOS 10.15: Xcode 12.4, Windows 10: Visual Studio 2019