Moving y4m encoding functions into separate files.

Change-Id: I03f614872167841515a74740d654c008b60104a4
diff --git a/y4menc.h b/y4menc.h
new file mode 100644
index 0000000..e5f7978
--- /dev/null
+++ b/y4menc.h
@@ -0,0 +1,27 @@
+/*
+ *  Copyright (c) 2014 The WebM project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef Y4MENC_H_
+#define Y4MENC_H_
+
+#include <stdio.h>
+
+#include "./tools_common.h"
+
+#include "vpx/vpx_decoder.h"
+
+void y4m_write_file_header(FILE *file, int width, int height,
+                           const struct VpxRational *framerate,
+                           vpx_img_fmt_t fmt);
+
+void y4m_write_frame_header(FILE *file);
+
+
+#endif  // Y4MENC_H_