Google doc strings

[helpmefindaname]

Use flake8-pydocstrings to enforce that existing doc strings follow the google docs format. And fix the format wherever it is not correctly following the google doc string format.

Current todo list:

• flair/datasets/biomedical.py
• flair/datasets/document_classification.py
• flair/datasets/entity_linking.py
• flair/datasets/sequence_labeling.py

[alanakbik]

Thanks @helpmefindaname this looks really good!

Lazydocs throws some errors, but mostly in the test classes:

Failed to generate docs for module flair.models.regexp_tagger: AttributeError("module 'flair.models.regexp_tagger' has no attribute '__create_fn__'")

Failed to generate docs for module tests.embeddings.test_document_transform_word_embeddings: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.embeddings.test_tfidf_embeddings: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.model_test_utils: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_entity_linker: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_relation_classifier: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_relation_extractor: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_sequence_tagger: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_tars_classifier: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_tars_ner: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_text_classifier: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_text_regressor: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.models.test_word_tagger: TypeError('super(type, obj): obj must be an instance or subtype of type')
Failed to generate docs for module tests.test_trainer: TypeError('super(type, obj): obj must be an instance or subtype of type')

But I think this is something for a future PR.