refactor: 更改项目目录结构

docs/chapters/Abstract.tex

docs/chapters/Achievements.tex

docs/chapters/Acknowledgement.tex

docs/chapters/Bibliography.tex

docs/chapters/Environments.tex

docs/chapters/FigTabCode.tex

docs/chapters/Introduction.tex

docs/chapters/Layout.tex

docs/chapters/Mathematics.tex

docs/chapters/Preface.tex

docs/chapters/Reference.tex

docs/chapters/Standard.tex

docs/njuthesis-sample.bib

docs/njuthesis-sample.tex

docs/njuvisual.sty

source/README-CTAN.md

source/latexmkrc

source/njuthesis.dtx