Remove OrderedXmlMarkup class

This class adds nothing to the Cucumber library itself. It exists only to help
with testing.
Fix JUnit features after removing OrderedXmlMarkup class
Remove unsupported Ruby version code

Ruby 1.8 is not supported anymore.
Merge pull request #566 from jimvm/unsupported_version_code

Remove unsupported Ruby version code
Merge pull request #561 from jimvm/ordered_xml_markup

Remove OrderedXmlMarkup class