move src/extras to the top-level

reserve src/ for the code of the main libraries: libwebp, libwebpdemux
and libwebpmux

+ demote this library to internal only; i.e., don't install the header +
lib with make install

Change-Id: I8c9844db8f494be0fa0a2549a5b75b5cebcf666d

extras/extras.h

@@ -0,0 +1,51 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING 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 WEBP_WEBP_EXTRAS_H_
+#define WEBP_WEBP_EXTRAS_H_
+
+#include "webp/types.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "webp/encode.h"
+
+#define WEBP_EXTRAS_ABI_VERSION 0x0000    // MAJOR(8b) + MINOR(8b)
+
+//------------------------------------------------------------------------------
+
+// Returns the version number of the extras library, packed in hexadecimal using
+// 8bits for each of major/minor/revision. E.g: v2.5.7 is 0x020507.
+WEBP_EXTERN(int) WebPGetExtrasVersion(void);
+
+//------------------------------------------------------------------------------
+// Ad-hoc colorspace importers.
+
+// Import luma sample (gray scale image) into 'picture'. The 'picture'
+// width and height must be set prior to calling this function.
+WEBP_EXTERN(int) WebPImportGray(const uint8_t* gray, WebPPicture* picture);
+
+// Import rgb sample in RGB565 packed format into 'picture'. The 'picture'
+// width and height must be set prior to calling this function.
+WEBP_EXTERN(int) WebPImportRGB565(const uint8_t* rgb565, WebPPicture* pic);
+
+// Import rgb sample in RGB4444 packed format into 'picture'. The 'picture'
+// width and height must be set prior to calling this function.
+WEBP_EXTERN(int) WebPImportRGB4444(const uint8_t* rgb4444, WebPPicture* pic);
+
+//------------------------------------------------------------------------------
+
+#ifdef __cplusplus
+}    // extern "C"
+#endif
+
+#endif  /* WEBP_WEBP_EXTRAS_H_ */