bump to v1.2.0

- 预发布版本使用形如 "`[1.0.2-rc.1] - 2021-06-11`" 作为二级标题，

- 正式发布版本使用形如 "`[1.0.1] - 2020-07-25`" 作为二级标题。

## [1.2.0] - 2021-07-04

## [1.2.0] - 2021-06-30

## Added

- 添加使用文档 `sustechthesis.pdf`

- 改回 `dtx` 文件生成 `cls` 文件的形式，`dtx` 文件内内有大量的注释方便后期维护。

### Changed

- 更改封面英文标题为自动大写

%

% \iffalse

%<*driver>

\ProvidesFile{sustechthesis.dtx}[2021/06/15 1.2.0 Southern University of Science and Technology Thesis Template]

\ProvidesFile{sustechthesis.dtx}[2021/06/30 1.2.0 Southern University of Science and Technology Thesis Template]

\documentclass{ltxdoc}

\usepackage{dtx-style}

\EnableCrossrefs

%    \begin{macrocode}

%<cls>\NeedsTeXFormat{LaTeX2e}[2017/04/15]

%<cls>\ProvidesClass{sustechthesis}

%<cls>[2021/06/15 1.2.0 Southern University of Science and Technology Thesis Template]

%<cls>[2021/06/30 1.2.0 Southern University of Science and Technology Thesis Template]

%    \end{macrocode}

%

% 报错