Cleanup

Shell for test FTP server can now list and close connections

Copied ReadLine into third-party and changed to allow async auto completion handlers.

Fixed warnings around nullable reference types

Wait for the task to be running.

Fixes #75
Fixes #76

Update to 4.5.1 due to security alert on GitHub

Make IFtpCommandHandlerExtensionScanner scoped

Fixes #72

Handle unknown user/group IDs

Fixed unit test

Removed dead code

Unix file system implementation is complete