Release 0.25.0

This release includes a long-standing request being finally fulfilled (part of #7). We now support Stochastic Gradient Descent!

Full changelog:

-  Added support for `SGDClassifier` and `SGDRegressor`
-  Added option to use FeatureHasher instead of DictVectorizer to make learning with feature sets that have millions of features possible.
-  Minor documentation fix for `generate_predictions`.


All the credit for this release goes to @nineil. Thanks Nils!