GTK 练习代码 (MAC 系统)

<h2>安装<h2>
- 输入命令 `brew install gtk+3`
- 查看安装结果 `pkg-config --list-all | grep gtk`, 出现下面结果，说明安装成功
  ```shell
    gtk+-3.0                            GTK+ - GTK+ Graphical UI Library
    gtk+-unix-print-3.0                 GTK+ - GTK+ Unix print support
    gtk+-quartz-3.0                     GTK+ - GTK+ Graphical UI Library
```