* 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