add support for HKEY_CLASSES_ROOT

[joachimmetz]

• initially directly map this to HKEY_LOCAL_MACHINE\Software\Classes ?
• https://msdn.microsoft.com/en-us/library/windows/desktop/ms724475%28v=vs.85%29.aspx
• https://msdn.microsoft.com/en-us/library/windows/desktop/ms724498%28v=vs.85%29.aspx