C API: Add SK_API, also documentation of an example.

include/c/sk_image.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 // EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL EXPERIMENTAL
 // DO NOT USE -- FOR INTERNAL TESTING ONLY
 
 #ifndef sk_image_DEFINED
 #define sk_image_DEFINED
 
 #include "sk_types.h"
 
 SK_C_PLUS_PLUS_BEGIN_GUARD
 
 /**
  *  Return a new image that has made a copy of the provided pixels, or NULL on failure.
  *  Balance with a call to sk_image_unref().
  */
-sk_image_t* sk_image_new_raster_copy(const sk_imageinfo_t*, const void* pixels, size_t rowBytes);
+SK_API sk_image_t* sk_image_new_raster_copy(const sk_imageinfo_t*, const void* pixels, size_t rowBytes);
 
 /**
  *  If the specified data can be interpreted as a compressed image (e.g. PNG or JPEG) then this
  *  returns an image. If the encoded data is not supported, returns NULL.
  *
  *  On success, the encoded data may be processed immediately, or it may be ref()'d for later
  *  use.
  */
-sk_image_t* sk_image_new_from_encoded(const sk_data_t* encoded, const sk_irect_t* subset);
+SK_API sk_image_t* sk_image_new_from_encoded(const sk_data_t* encoded, const sk_irect_t* subset);
 
-sk_data_t* sk_image_encode(const sk_image_t*);
+SK_API sk_data_t* sk_image_encode(const sk_image_t*);
 
-void sk_image_ref(const sk_image_t*);
-void sk_image_unref(const sk_image_t*);
-int sk_image_get_width(const sk_image_t*);
-int sk_image_get_height(const sk_image_t*);
-uint32_t sk_image_get_unique_id(const sk_image_t*);
+SK_API void sk_image_ref(const sk_image_t*);
+SK_API void sk_image_unref(const sk_image_t*);
+SK_API int sk_image_get_width(const sk_image_t*);
+SK_API int sk_image_get_height(const sk_image_t*);
+SK_API uint32_t sk_image_get_unique_id(const sk_image_t*);
 
 SK_C_PLUS_PLUS_END_GUARD
 
 #endif