将HTML Source String转为NSAttributedString
iOS自带的渲染HTML的- (instancetype)initWithData:options:documentAttributes:error:方法速度太慢，所以自己先实现一个简易的解析工具，目前只支持<font>和<strike>标签来设置字符串样式。
- 需要在header search paths里添加
/usr/include/libxml2 - 需要在二进制库里添加 libxml2.tbd
##Usage:
NSString *htmlString = @"<font color='#00ff00' bgcolor='#00ffff'>bai<font size='24' color='#ff00ff'>This <strike>is aaa</strike> some text!</font>bai</font><font color='#000000'>价格：</font><font color='#00ffff'>33.4</font><font color='#00ff00'>bai<font size='24' color='#ff00ff'>This <strike>is aaa</strike> some text!</font>bai</font><font color='#000000'>价格：</font><font color='#00ffff'>33.4</font><font color='#00ff00'>bai<font size='24' color='#ff00ff'>This <strike>is aaa</strike> some text!</font>bai</font><font color='#000000'>价格：</font><font color='#00ffff'>33.4</font><font color='#00ff00'>bai<font size='24' color='#ff00ff'>This <strike>is aaa</strike> some text!</font>bai</font><font color='#000000'>价格：</font><font color='#00ffff'>33.4</font><font color='#00ff00'>bai<font size='24' color='#ff00ff'>This <strike>is aaa</strike> some text!</font>bai</font><font color='#000000'>价格：</font><font color='#00ffff'>33.4</font>";
label.attributedText = [[HTMLParser sharedInstance] parseHTMLWithString:htmlString error:nil];