* Remove deprecated option enable_auto_doc_ref for recommonmark
* Add first level navigation structure for Nano how-to guides
* Update navigation for How-to Training part
* Update navigation for How-to Inference part
* Update navigation for How-to Preprocessing/Install part and other small fixes
* Fix wrong link path caused by position changes of how-to install related guides
* Small fix
* Restyle blockquote elements in web
* Add a generalized how-to section for preprocessing, including the data process accelerastion for PyTorch
* Small fix
* Update based on comments and small typo fixes
* Small fixes
* Rearrange file structure for PyTorch Inference for docs and add titles for PyTorch-Lightning Training
* Add How-to guide: How to accelerate a PyTorch-Lightning application on training workloads through Intel® Extension for PyTorch*
* Add how-to guide: How to accelerate a PyTorch-Lightning application on training workloads through multiple instances
* Revise: remove '-' in 'PyTorch-Lightning' and some other changes
* Add How-to guides: How to use the channels last memory format in your PyTorch Lightning application for training
* Add how-to guide: Use BFloat16 Mixed Precision for PyTorch Lightning Training
* Add How-to guide: How to accelerate a computer vision data processing pipeline
* Small Revision: change comments in several code cells
* Disable other nano tests temporarily
* Add github action tests for Nano Training PyTorch Lightning tests
* Enable other nano tests again
* Small revisions: typos and explanation texts changes
* Revise: update based on comments
