url出现特殊字符，需要进行编码

1） 网络访问请求：中文空格字符编码/解码

        stringByAddingPercentEscapesUsingEncoding(只对 `#%^{}[]|\"<> 加空格共14个字符编码，不包括”&?”等符号), ios9将淘汰，建议用stringByAddingPercentEncodingWithAllowedCharacters方法

        URLFragmentAllowedCharacterSet  "#%<>[\]^`{|}

        URLHostAllowedCharacterSet      "#%/<>?@\^`{|}

        URLPasswordAllowedCharacterSet  "#%/:<>?@[\]^`{|}

        URLPathAllowedCharacterSet      "#%;<>?[\]^`{|}

        URLQueryAllowedCharacterSet     "#%<>[\]^`{|}

        URLUserAllowedCharacterSet      "#%/:<>?@[\]^`

（2）网络访问请求：中文空格字符解码

        stringByRemovingPercentEncoding  ----  xcode7可能会提示要将stringByAddingPercentEscapesUsingEncoding替换成此方法，要根据是否是解码来区分

        */
        //代替stringByAddingPercentEscapesUsingEncoding

        let customAllowedSet =  NSCharacterSet(charactersInString:"`#%^{}\"[]|\\<> ").invertedSet

例如：

NSString *urlStr = [NSString stringWithFormat:@"%@/uploadFeedback?sessionID=%@&content=%@", kMainURL, [MySharedClass      sharedInstance].sessionID, _textView.text];

urlStr = [urlStr stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];