Add docstring for Trainer class.
Add docstring for Trainer class.

explosion/spaCy,raphael0202/spaCy,oroszgy/spaCy.hu,oroszgy/spaCy.hu,recognai/spaCy,raphael0202/spaCy,banglakit/spaCy,banglakit/spaCy,honnibal/spaCy,raphael0202/spaCy,spacy-io/spaCy,explosion/spaCy,spacy-io/spaCy,Gregory-Howard/spaCy,oroszgy/spaCy.hu,recognai/spaCy,spacy-io/spaCy,aikramer2/spaCy,raphael0202/spaCy,Gregory-Howard/spaCy,Gregory-Howard/spaCy,banglakit/spaCy,oroszgy/spaCy.hu,recognai/spaCy,Gregory-Howard/spaCy,honnibal/spaCy,honnibal/spaCy,Gregory-Howard/spaCy,explosion/spaCy,oroszgy/spaCy.hu,oroszgy/spaCy.hu,raphael0202/spaCy,banglakit/spaCy,banglakit/spaCy,Gregory-Howard/spaCy,aikramer2/spaCy,recognai/spaCy,explosion/spaCy,raphael0202/spaCy,honnibal/spaCy,explosion/spaCy,explosion/spaCy,spacy-io/spaCy,banglakit/spaCy,aikramer2/spaCy,spacy-io/spaCy,spacy-io/spaCy,recognai/spaCy,aikramer2/spaCy,aikramer2/spaCy,recognai/spaCy,aikramer2/spaCy