XMLUnit.NET 2.0.0-alpha-04

This is the third alpha release of XMLUnit.NET 2.0.0.

The implementation is considered stable enough for a production release. This is an alpha release as we need more people to try out the API in order to call it final.

Breaking Changes since 2.0.0-alpha-03

• the unused SchemaURI property of Validator has been removed.
• the mapping of IDifferenceEngine.NamespaceContext has been
  inverted from prefix -> URI to URI -> prefix in order to be
  consistent with the same concept in IXPathEngine.

Other Changes since 2.0.0-alpha-03

• Comparison now also contains the XPath of the parent of the
  compared nodes or attributes which is most useful in cases of
  missing nodes/attributes because the XPath on one side is null in
  these cases.
  Issue #48
  ported from PR #50
  by @eguib.