v0.4.0

• Add unsupervised context retriever for BertNamedEntityRecognizer
• Greatly improve GraphRulesCharacterUnifier performance
• Update documentation, with a new "Contributing" section
• Add some utilities to easily train a custom NER model
• Add a new french NER model! compnet-renard/bert-base-cased-literary-NER
• The characters_graph state attribute has been deprecated (use character_network instead)
• Add py.typed file to better support typing in external tools
• Update tibert to version 0.3.0
• Minor fixes