Simplify project files on repository homepage

[neoddish]

There are too many scattered project files in the root directory, and even the Readme cannot be seen on the first screen view. This is not conducive to users understanding AVA. Can we reasonably collapse the project files to make the overall project structure more simple and clear? Based on this, we can consider what more user-friendly introductions and promotions can be done on the readme page.

根目录的工程文件太多太碎了，打开 AVA 的 github 首页都看不到 Readme 了。这不太利于用户了解 AVA，看看能不能合理收起工程文件，让整个项目的结构更简单清晰。基于此，再去思考 readme 页面里能做哪些更友好的介绍和推广。