Added example for opinion mining
Merge pull request #23 from rafacarrascosa/develop

Bug fix, improved sample, added feature
Added stopwords for the opinion example
Added Classifier to the api to allow load from pickled
Merge pull request #24 from j0hn/develop

Added opinion mining example
Completed some docstrings
Merge pull request #25 from j0hn/develop

Completed some docstrings
Fixed bug in naivebayes (adding __len__ makes "if x:" work)
Unused variable
Bug fix, you cannot have target in tree