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add ICUNormalizer2CharFilter

Included ICUNormalizer2Charfilter in Lucene 4.8.0.
Add CharFilterFactory.

Now, char_filter name is "icu_normalizer", however token_filter name is same name.

Closes #27.
Add integration tests

Closes #31.
Update to Lucene 4.8 / Elasticsearch 1.2.0

Related to #24.