explosion/spaCy: v2.0.11: Alpha Vietnamese support, fixes to vectors, improved errors and more

📊 Help us improve spaCy and take the User Survey 2018! ✨ New features and improvements

• NEW: Alpha Vietnamese support with tokenization via Pyvi.
• NEW: Improved system for error messages and warnings. Errors now have unique error codes and are referenced in one place, and all unspecified asserts have been replaced with descriptive errors. See #2163 for implementation details, and let us know if you have any suggestions for errors and warnings in #2164!
• Improve language data for Polish.
• Tidy up dependencies and drop six, html5lib, ftfy and requests.
• Improve efficiency (and potentially accuracy) of beam-search training, by randomly using greedy updates for some sentences. This can be controlled by changing the beam_update_prob entry in nlp.parser.cfg. The default value is 0.5, so 50% of beam updates will be done as greedy updates.

• Fix issue #1554, #1752, #2159: Fix Token.ent_iob after Doc.merge(), and ensure consistency in Doc.ents.
• Fix issue #1660: Fix loading of multiple vector models.
• Fix issue #1967: Allow entity types with dashes.
• Fix issue #2032: Fix accidentally quadratic runtime in Vocab.set_vector.
• Fix issue #2050: Correct mistakes in Italian lemmatizer data.
• Fix issue #2073: Make Token.set_extension work as expected.
• Fix issue #2100, #2151, #2181: Drop six and html5lib and prevent dependency conflict with TensorFlow / Keras.
• Fix issue #2101: Improve error message if token text is empty string.
• Fix issue #2121: Fix Language.to_bytes and pickling in Thinc.
• Fix issue #2156: Fix hashtag example in Matcher docs.
• Fix issue #2177: Don't raise error in set_extension if getter and setter are specified or if default=None, and add error if setter is specified with no getter.

• Add example for TensorBoard's standalone embedding projector.
• Improve example for training a new entity type.
• Add formal CITATION for assigning a DOI via Zenodo.

Thanks to @jimregan, @justindujardin, @trungtv, @katrinleinweber and @skrcode for the pull requests and contributions.