v1.4.0 Data augmentation and optimization

This pretty big update brings data augmentation, some bug fixes and optimizations, allowing to write more elegant code.

Changes

• 8f201e0 308fb27 Data augmentation methods ! 🙌 They can be applied on both MIDI and tokens, to augment data by shifting the pitch, velocity and duration values.
• 1d8e903 You can perform data augmentation while tokenizing a dataset (tokenize_midi_dataset method) with the data_augment_offsets argument. This will be done at the token level, as its faster than augmenting MIDI objects.
• 0634ade BPE is now implemented in the main tokenizer class! This means all tokenizers can benefit form it in a much prettier way!
• 0634ade bpe method renamed to learn_bpe, and now returns metrics (that are also showed in the progress bar during the learning) on the number of token combinations and sequence length reduction
• 7b8c977 Retrocompatibility when loading tokenizer config files with BPE from older versions
• 3cea9aa @nturusin Example notebook of GPT2 Hugging Face music transformer: fixes in training
• 65afa6b The tokens_to_midi and save_tokens methods can now receive tokens as Tensors and numpy arrays. PyTorch, TensorFlow and Jax (numpy) tensors are supported. The convert_tokens_tensors_to_list decorator will convert them to lists, you can use it on your custom methods.
• aab64aa The __call__ magic method now automatically route to midi_to_tokens or tokens_to_midi following what you give it. You can now use more elegantly tokenizers as tokenizer(midi_obj) or tokenizer(generated_tokens).
• e90b20a Bugfix in Structured causing a possible infinite while loop with illegal token types successions
• 947af8c Big refactor of MuMIDI, which have now fixed vocab / type idx. It is easier to handle and use. (thanks @gonzaloarca)
• 947af8c CPWord "Ignore" tokens are all renamed Ignore_None by convention, making operations easier in data augmentation and other methods.

Compatibility

• code with BPE would have to updated: remove bpe(tokenizer) and just declare tokenizers normally, rename the bpe method to learn_bpe
• MuMIDI tokens and tokenizers will be incompatible with v1.4.0