Deprecate smartcn_word

Looks like `WordTokenFilter` has been [deprecated in Lucene 4.8](http://lucene.apache.org/core/4_8_0/analyzers-smartcn/org/apache/lucene/analysis/cn/smart/WordTokenFilter.html) and looking at the javadoc, it looks like that only the [HMMChineseTokenizer](http://lucene.apache.org/core/4_8_0/analyzers-smartcn/org/apache/lucene/analysis/cn/smart/HMMChineseTokenizer.html) will be supported.

We need to deprecate `smartcn_word` and `smartcn_sentence`.
We add `smartcn_tokenizer` which does the both things.

 Closes #22.