Speedy lammatization, Reuters-21578 corpus and modified ESA model

I added a light flag for speedy lammatization. The flag lets the lemmatizer use a different algorithm from the pattern library.

The request also includes a class to handle Reuters-21578 dataset as corpus. The class is not fully tested, yet. Also the SQL should be overlooked.
The interface might change.

I also added the implementation of my modified ESA model. It requires the selectkbest modul. For now I put it in the models folder.