moved enum decoder_command to decoder_api.h

The decoder plugins need this type, so export it in the public API.
This allows is to remove "decode.h" from "decoder_api.h", uncluttering
the API namespace some more.

src/decode.h

@@ -19,6 +19,7 @@
 #ifndef DECODE_H
 #define DECODE_H
 
+#include "decoder_api.h"
 #include "song.h"
 
 #include "audio_format.h"
@@ -33,13 +34,6 @@ enum decoder_state {
 	DECODE_STATE_DECODE
 };
 
-enum decoder_command {
-	DECODE_COMMAND_NONE = 0,
-	DECODE_COMMAND_START,
-	DECODE_COMMAND_STOP,
-	DECODE_COMMAND_SEEK
-};
-
 #define DECODE_ERROR_NOERROR	0
 #define DECODE_ERROR_UNKTYPE	10
 #define DECODE_ERROR_FILE	20

src/decoder_api.h

@@ -30,7 +30,6 @@
 #include "replayGain.h"
 #include "tag.h"
 #include "playerData.h"
-#include "decode.h"
 
 
 /* valid values for streamTypes in the InputPlugin struct: */
@@ -38,6 +37,14 @@
 #define INPUT_PLUGIN_STREAM_URL		0x02
 
 
+enum decoder_command {
+	DECODE_COMMAND_NONE = 0,
+	DECODE_COMMAND_START,
+	DECODE_COMMAND_STOP,
+	DECODE_COMMAND_SEEK
+};
+
+
 struct decoder;