0.1.0.4
	* fixed generated xml so it gets read by MS Excel with no warnings (thanks Dmitriy Nikitinskiy <nick@linux-i294.site>)
	* improved shared strings collection by using Vector (thanks Dmitriy Nikitinskiy <nick@linux-i294.site>)
	* empty xml elements don't get emmitted anymore (thanks Philipp Hausmann <ph_git@314.ch>)
	* imporoved and cleaned up core.xml generation
0.1.0.3
	* added "str" cells content extraction as text
	* added a notice that formulas in <f> are not yet supported
0.1.0
	* better tests and documentation
	* lenses for worksheets/cells
	* removed streaming support as it needs better API and improved implementaion
	* removed CellLocalTime as ambiguous, added CellBool
0.0.1
	* initial release