Hotfix-2 to 4.1.2

Install dotnet for NuGet pipeline

Fixed some typos and a bug

Version 4.0.0.

Version 3.7.3.

Version 3.7.2.

Corrected a typo in a comment.

Renamed HEXL to hexl in pkgconfig.

Edited CHANGES.md.

Removed installation of clang-9 from nix pipeline.