First part of the patch: add option --load

Option --load makes espeak-ng consider the voice name provided a name of
a file relative to the current directory.

Signed-off-by: golubovsky <golubovsky@gmail.com>

src/include/espeak-ng/speak_lib.h

@@ -606,6 +606,19 @@ ESPEAK_API const espeak_VOICE **espeak_ListVoices(espeak_VOICE *voice_spec);
    are listed, and they are listed in preference order.
 */
 
+#ifdef __cplusplus
+extern "C"
+#endif
+ESPEAK_API espeak_ERROR espeak_SetVoiceByFile(const char *filename);
+/* Loads a voice given the file path.  Language is not considered.
+   "filename" is a UTF8 string.
+
+   Return: EE_OK: operation achieved
+           EE_BUFFER_FULL: the command can not be buffered;
+             you may try after a while to call the function again.
+	   EE_INTERNAL_ERROR.
+*/
+
 #ifdef __cplusplus
 extern "C"
 #endif