Based on transformers v4.17.0

New

Efficient Fine-Tuning Methods

• Add Prefix Tuning (@calpt via #292)
• Add Parallel adapters & Mix-and-Match adapter (@calpt via #292)
• Add Compacter (@hSterz via #297)

Misc

• Introduce XAdapterModel classes as central & recommended model classes (@calpt via #289)
• Introduce ConfigUnion class for flexible combination of adapter configs (@calpt via #292)
• Add AdapterSetup context manager to replace adapter_names parameter (@calpt via #257)
• Add ForwardContext to wrap model forward pass with adapters (@calpt via #267, #295)
• Search all remote sources when passing source=None (new default) to load_adapter() (@calpt via #309)

Changed

• Deprecate XModelWithHeads in favor of XAdapterModel (@calpt via #289)
• Refactored adapter integration into model classes and model configs (@calpt via #263, #304)
• Rename activation functions to match Transformers' names (@hSterz via #298)
• Upgrade of underlying transformers version (@calpt via #311)

Fixed

• Fix seq2seq generation with flexible heads classes (@calpt via #275, @hSterz via #285)
• Parallel composition for XLM-Roberta (@calpt via #305)