Minor improvements and fixes.

This project is now turned into Go module, which meas it is possible to be used by another Go module. See example for starting a file server by invoking ghfs as a library. Note ghfs does not follow semantic versioning strictly.

次要改进和修复。

此项目已转化为Go模块，即它可以被另一个Go模块所使用。查看示例，它把ghfs作为库调用启动一个文件服务器。注意ghfs不严格遵守语义化版本。