TODO:
- Iterators for element nodes
- Allow whitespace between attribute name, "=" and value
- Add a helper class to fix the formatting of an XML document

DONE:
* Add copyright information to all files
* A class which can decode an arbitrary InputStream using the standard XML rules
* Documentation
* Add a tutorial to the docs
* Add support for entity references
* Extend ProcessingInstruction to really support XML declarations
* Add support for parsing DOCTYPE