Added proper Exception handling using `UserServiceException` and
`Exception`.
Reworked Endpoint to not be so fragmented. XML Formatter is now the
default `MessageFormatter`.
refs #44
Removed UTF-8 decoding from prettyxml printer since it's no longer
needed.
See the previous commit:Endpoint for where the response is now properly printed in
UTF-8.
Updated test answers to match the new error messages being returned.
refs #44, #38