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 <strong>NEW:</strong> Alpha Vietnamese support with tokenization via Pyvi. <strong>NEW:</strong> Improved system for error messages and warnings. Errors now have unique error codes and are referenced in one place, and all unspecified <code>assert</code>s 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 <code>six</code>, <code>html5lib</code>, <code>ftfy</code> and <code>requests</code>. Improve efficiency (and potentially accuracy) of beam-search training, by randomly using greedy updates for some sentences. This can be controlled by changing the <code>beam_update_prob</code> entry in <code>nlp.parser.cfg</code>. The default value is 0.5, so 50% of beam updates will be done as greedy updates. 🔴 Bug fixes Fix issue #1554, #1752, #2159: Fix <code>Token.ent_iob</code> after <code>Doc.merge()</code>, and ensure consistency in <code>Doc.ents</code>. 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 <code>Vocab.set_vector</code>. Fix issue #2050: Correct mistakes in Italian lemmatizer data. Fix issue #2073: Make <code>Token.set_extension</code> work as expected. Fix issue #2100, #2151, #2181: Drop <code>six</code> and <code>html5lib</code> and prevent dependency conflict with TensorFlow / Keras. Fix issue #2101: Improve error message if token text is empty string. Fix issue #2121: Fix <code>Language.to_bytes</code> and pickling in Thinc. Fix issue #2156: Fix hashtag example in <code>Matcher</code> docs. Fix issue #2177: Don't raise error in <code>set_extension</code> if <code>getter</code> and <code>setter</code> are specified or if <code>default=None</code>, and add error if <code>setter</code> is specified with no <code>getter</code>. 📖 Documentation and examples Add example for TensorBoard's standalone embedding projector. Improve example for training a new entity type. Add formal <code>CITATION</code> for assigning a DOI via Zenodo. 👥 Contributors Thanks to @jimregan, @justindujardin, @trungtv, @katrinleinweber and @skrcode for the pull requests and contributions.