nagisa v0.2.0

nagisa 0.2.0 incorporates the following changes:

• Provide a simple train method for a joint word segmentation and sequence labeling (e.g, POS-tagging, NER) model.
• Fix ZeroDivisionError in mecab_system_eval.py.

nagisa v0.1.2

nagisa 0.1.2 incorporates the following changes:

• Provide the postagging method #8
• Adopt the longest match to extract a word in nagisa.Tagger(single_word_list)