### What problem were solved in this pull request?

Problem:
当前生成的github pages不太整洁方便，可以优化一下

### What is changed and how it works?
改用mdbook生成文档，并整理文档目录，调整链接

### What problem were solved in this pull request?

Issue Number: close #175 

Problem:
github page 构建失败
看到报错信息：
```
googletest/docs/assets/css/style.scss File to import not found or unreadable
```
本来miniob的pages与子模块是无关的，看github page
action的逻辑是checkout了子模块，而这个子模块在这里有点问题。

### What is changed and how it works?
把github pages改成github action模式构建，并修改checkout的submodules参数为false，即不拉子模块。
这里只是修改一些文档链接，gitub page相关的commit：

https://github.com/oceanbase/miniob/commit/8a33f5219d7ed27797d49dc2a9bfd945dcd0d327

### Other information

增加MiniOB介绍、训练营输出约定、SQL词法语法解析文档