Update VirtualBox.xidl - includes enum for IMachine.paravirt_provider.
IAppliance and VirtualSystemDescription extension to help with importing new appliances.  Solution for issue #15.
This change attempts to address issue #14 by making the attribute behaviour more explicit. *value* is not optional.
Expose a fixed set of VirtualSystemDescription appliance value setters.
Include latests extension classes in library.rst.  Include automod doc for library_base.py
update doc.
Order autodoc by source ref
Improve error construction and decoding.
Link doc class return error type classes.  Define the basic ole types which are defined in VirtualBox.xidl.
Add doc to set_final_value
remove verbose name for raises in doc.
Added raises doc and fleshed out references to ole execption types
Error raises test