1.3.0

• The Service class adds a new mapValueObject method which provides basic
  capabilities to map between ValueObjects and XML.
• #61: You can now specify serializers for specific classes, allowing you
  separate the object you want to serialize from the serializer. This uses the
  $classMap property which is defined on both the Service and Writer.
• It's now possible to pass an array of possible root elements to
  Sabre\Xml\Service::expect().
• Moved some parsing logic to Reader::getDeserializerForElementName(),
  so people with more advanced use-cases can implement their own logic there.
• #63: When serializing elements using arrays, the value key in the array is
  now optional.
• #62: Added a keyValue deserializer function. This can be used instead of
  the Element\KeyValue class and is a lot more flexible. (@staabm)
• Also added an enum deserializer function to replace
  Element\Elements.
• Using an empty string for a namespace prefix now has the same effect as
  null.