Merge branch 'add_audio_extractor' into 'master'

.gitignore

bob/learn/pytorch/__init__.py

bob/learn/pytorch/architectures/DltResNet.py

bob/learn/pytorch/architectures/ResNet.py

bob/learn/pytorch/architectures/utils.py

bob/learn/pytorch/extractor/__init__.py

bob/learn/pytorch/extractor/audio/DummyExtractor.py

bob/learn/pytorch/extractor/audio/__init__.py

bob/learn/pytorch/preprocessor/__init__.py

bob/learn/pytorch/preprocessor/audio/DltResNet.py

bob/learn/pytorch/preprocessor/audio/__init__.py

bob/learn/pytorch/test/test_audio_extractor.py

conda/meta.yaml

doc/guide_audio_extractor.rst

doc/index.rst

doc/py_api.rst

requirements.txt