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

Problem:
There is no mysql protocol document

### What is changed and how it works?
add a mysql protocol document.

### Other information

### 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