Add watch support on Windows

Pull https://github.com/jasonrogena/librarian/pull/3 added support for directory watching on Linus and macOS. Support for Windows wasn't added because some tests failed on Windows and I don't have a Windows machine to debug. Here's [an example run](https://github.com/jasonrogena/librarian/runs/6889668281?check_suite_focus=true) with the failing tests.