GitLab

* [Docs] Refactor the structure of documentation

* [Docs] Refactor the structure of documentation

* fix symlink

* fix link

* fix typo

* polish docstring

* fix docstring

* [Fix] Fix pdf error when building docs

* fix docs

* fix pdf

* fix pdf

* fix pdf

* [Docs] Refactor documentation

* [Docs] Refactor documentation

* refactor docs

* refactor docs

* set sphinx==3.1.2

* fix typo

* modify according to comment

* modify according to comment

* modify according to comment

* [Docs] delete unnecessary file

* fix title

* rename

* rename