raise a single error for an unknown service/port
changed wsdl#services to respect law of demeter
render complex types w/o children as self-closing

fixes #477
added rake :graph task

generates and opens (os x) a dependency graph via the rubydeps gem.
don't install rubydeps on ci
moved xml-related objects into its own namespace
updated the gemspec
added license information to the gemspec [ci skip]