服务端返回的不一定都是纯字符串，有可能是带有HTML标签的
//html字符串转换为富文本
NSString *html = @"<p style='color:green'>首付<span style='color:#e83c36;'>5000元</span>，提前付<span style='color:red'>3倍月供</span>，月供<span style='color:red'>3000元</span>(48期)</p>";
NSAttributedString *attStr = [[NSAttributedString alloc] initWithData:[html dataUsingEncoding:NSUnicodeStringEncoding] options:@{NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType} documentAttributes:nil error:nil];
//富文本转换为html字符串
//富文本转换为html(最后相当于整个网页代码，会有css等)
NSDictionary *dic = @{NSDocumentTypeDocumentAttribute:NSHTMLTextDocumentType,NSCharacterEncodingDocumentAttribute:@(NSUnicodeStringEncoding)};
NSData *data = [attStr dataFromRange:NSMakeRange(0, attStr.length) documentAttributes:dic error:nil];
NSString *str = [[NSString alloc] initWithData:data encoding:NSUnicodeStringEncoding];
