Fairly massive update

- XMLWriterPlus is now an implementation of PHP's native XMLWriter class
- Added ability to append indexed Lists (integer-indexed arrays) or Hash's (string-indexed arrays / objects) to the XML document
- Updated README.md slightly with some examples of new features / changes.
Merge branch 'master' of https://github.com/dcarbone/xml-writer-plus

Conflicts:
	README.md