modify importance function
Merge branch 'master' of https://github.com/trondarild/applied-ai
fix could not establish classification node error
fix buges in decisiontree.py
Merge branch 'master' of https://github.com/trondarild/applied-ai

Conflicts:
	decision-trees/decisiontree.py
	decision-trees/importance.py
	decision-trees/readarff.py

fix bugs with display small trees