Changes in 0.0.5:
	- Better reporting of NA values in factor features.
	- Order cache removed as it was both incorrect and not
	actually providing substantial speed-ups.

Changes in 0.0.4:
	* This version is incorrect; please do not use.
	- Memory leak fixed; thanks to Tony Auckland for spotting.
	- Fixed regression on integer decisions.
	- Integer midpoint between a & b is now floor((a+b)/2)
	rather than min(a,b).
	- Improved error reporting with extract_forest().
	- Order caching for faster training on long numeric features.

Changes in 0.0.3:
	* This version has a memory leak.
	- First public release.