XMLUnit.NET 2.10.0 Released

• adjusted the NUnit 3.x constraints so they should work for NUnit 4.x as well.
  Issue #40.

• add a new ElementSelectors.ByNameAndAllAttributes variant that filters attributes before deciding whether elements can be compared.
  Inspired by Issue #xmlunit/259

• Nodes.GetMergedNestedText and Nodes.StripElementContentWhitespace had the same problem of not knowning about XmlWhitespace that caused Issue #38. And neither of the methods could deal with XmlSignificantWhitespace at all.

• add XmlWhitespaceStrippedSource, XmlWhitespaceNormalizedSource, and XmlElementContentWhitespaceStrippedSource that only trim characters that are considered whitespace by the XM Specification from textual content.
  Also added new modifiers to DiffBuilder that make use of the new ISource types.
  Issue #39.