Fixes on TwDocument.save()

* TwDocument.save () works, requires Unit Testing to check output
* Fixed TwDocument.namespaces implementation
* Fixed any TwNode should have its own namespaces, but search one defined in
  TwDocument to use or add new local and at document
* Added DEBUG information on TwDocument.save()
* Removed initialize Xml.TextReader
* Fixes when DEBUG is enable