API changes:
* class jieba.Tokenizer, jieba.posseg.POSTokenizer
* class jieba.analyse.TFIDF, jieba.analyse.TextRank
* global functions are mapped to jieba.(posseg.)dt, the default (POS)Tokenizer
* multiprocessing only works with jieba.(posseg.)dt
* new lcut, lcut_for_search functions that returns a list
* jieba.analyse.textrank now returns 20 items by default
Tests:
* added test_lock.py to test multithread locking
* demo.py now contains most of the examples in README
Dingyuan Wang