Tablib

* Reverting methods back to properties.
* Windows bug compensated in documentation.

* Renamed DataBook Databook for consistency.
* Export properties changed to methods (XLS filename / StringIO bug).
* Optional Dataset.xls(path='filename') support (for writing on windows).
* Added utf-8 on the worksheet level.

* Updated unicode export for XLS.
* More exhaustive unit tests.

* Added Dataset.append() support for columns.

* Fixed Dataset.append() error on empty dataset.
* Updated Dataset.headers property w/ validation.
* Added Testing Fixtures.

* Packaging hotfixes.