Release notes

#188 - Make OperatingSystem instances available in public API.

#189 - Provide Downloaders that are not version-based.

Internal implementations of OperatingSystem have been renamed i.e., Windows is not DefaultWindows. This should not really be a problem unless a plugin implementation has reached into the implementation. If so, those plugins should be updated to use the toplevel interfaces instead i.e., org.ysb33r.grolifant5.api.core.os.Windows.instance().