Added tokens, tokens_arr and json for offline recongnizer result (#936)

Co-authored-by: leo <webmaster@360converter.com>

sherpa-onnx/c-api/c-api.h

@@ -481,7 +481,27 @@ SHERPA_ONNX_API typedef struct SherpaOnnxOfflineRecognizerResult {
 
   // number of entries in timestamps
   int32_t count;
-  // TODO(fangjun): Add more fields
+
+  // Pointer to continuous memory which holds string based tokens
+  // which are separated by \0
+  const char *tokens;
+
+  // a pointer array containing the address of the first item in tokens
+  const char *const *tokens_arr;
+
+  /** Return a json string.
+   *
+   * The returned string contains:
+   *   {
+   *     "text": "The recognition result",
+   *     "tokens": [x, x, x],
+   *     "timestamps": [x, x, x],
+   *     "segment": x,
+   *     "start_time": x,
+   *     "is_final": true|false
+   *   }
+   */
+  const char *json;
 } SherpaOnnxOfflineRecognizerResult;
 
 /// Get the result of the offline stream.