GetUserData is complete with tests

The GetUserData() service, implemented at Account.GetUserPreferences(), is now complete, to the extent possible. I added tests for all properties, which translate the values returned from Yahoo! to .NET objects.

If you look at the code you'll see several commented out properties. These are mostly undocumented properties, which I could only guess at what they mean. I may investigate them more later.

This marks half way to version 0.2, which will have complete get and set of user preferences.

The documentation was updated to reflect the new additions. Its looks was also upgraded, as I use a newer version of Doxygen to generate it.