decoder_api: added function decoder_timestamp()

Remove the data_time parameter from decoder_data().  This patch
eliminates the timestamp counting in most decoder plugins, because the
MPD core will do it automatically by default.

src/decoder_api.h

@@ -114,6 +114,15 @@ size_t
 decoder_read(struct decoder *decoder, struct input_stream *is,
 	     void *buffer, size_t length);
 
+/**
+ * Sets the time stamp for the next data chunk [seconds].  The MPD
+ * core automatically counts it up, and a decoder plugin only needs to
+ * use this function if it thinks that adding to the time stamp based
+ * on the buffer size won't work.
+ */
+void
+decoder_timestamp(struct decoder *decoder, double t);
+
 /**
  * This function is called by the decoder plugin when it has
  * successfully decoded block of input data.
@@ -129,7 +138,7 @@ decoder_read(struct decoder *decoder, struct input_stream *is,
 enum decoder_command
 decoder_data(struct decoder *decoder, struct input_stream *is,
 	     const void *data, size_t length,
-	     float data_time, uint16_t bitRate,
+	     uint16_t kbit_rate,
 	     struct replay_gain_info *replay_gain_info);
 
 /**