CRXHTMLTextView OC富文本转html标签输入框 感谢以下开源及网站思路： https://github.com/devxoul/UITextView-Placeholder http://www.jianshu.com/p/85d59410d3df https://github.com/songguolin/RichTextView https://github.com/lfb-cd/TextEditorDemo
