Heavy refactoring. These are more or less complete now. Small additions remain...

Heavy refactoring. These are more or less complete now. Small additions remain to make the interface more obvious for users.

From: fred.mailhot <fred.mailhot@cb17146a-f446-4be1-a4f7-bd7c5bb65646>

git-svn-id: https://scikit-learn.svn.sourceforge.net/svnroot/scikit-learn/trunk@31 22fbfee3-77ab-4535-9bad-27d1bd3bc7d8