* add docs for custom dataset, reader and model technical

* modify docs according to review, test=document_fix

* modify READER.md, test=document_fix

* unify log_smooth_windows and log_iter

test=develop

* remove duplicate log_iter

* remain mobile yml, since they are soft-link

test=develop

* fix some docs link error

* rename config_doc

* fix all documentation

* fix docs conf.py

* fix some error

* fix readthedocs