Extended SharpCompress.Common.ExtractionOptions with a delegate to write symbolic links. If not is null, and a symbolic link is encountered, an exception is thrown.
Removed Mono.Posix.NETStandard from the library, but added to the .NET Core 2.1 test application.
Extended the test to implement the delegate.
Extracts linkname from the tar header, and exposes this on IEntry as the LinkTarget (string) property. If an entry is not a symlink, then that property is null.
Uses Mono.Posix.NETStandard nuget to create a symlink. However, this is only applicable to .NET standard 2.0+. So far, unable to find a nuget that works for older versions.
Also, not sure what to do on Windows.