自己实现的文本编辑器，支持一下操作：向前翻页，向后翻页，删除已有内容，添加插入新内容，移动光标，保存或另存更改后的文本文件-Achieve their own text editor, support what operation: forward flip, back flip, delete the existing content, add new content to insert, move the cursor, Save or Save the changed text file