Textblob

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- Importing TextBlob is now **much faster**. This is because the noun phrase parsers are trained only on the first call to ``noun_phrases`` (instead of training them every time you import TextBlob).
- Add text.taggers module which allows user to change which POS tagger implementation to use. Currently supports PatternTagger and NLTKTagger (NLTKTagger only works with Python 2).
- NPExtractor and Tagger objects can be passed to TextBlob's constructor.
- Fix bug with POS-tagger not tagging one-letter words.
- Rename text/np_extractor.py -> text/np_extractors.py
- Add run_tests.py script.

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- Every word in a ``Blob`` or ``Sentence`` is a ``Word`` instance which has methods for inflection, e.g ``word.pluralize()`` and ``word.singularize()``.

- Updated the ``np_extractor`` module. Now has an new implementation, ``ConllExtractor`` that uses the Conll2000 chunking corpus. Only works on Py2.