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

include/c/sk_data.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_data_DEFINED
 #define sk_data_DEFINED
 
 #include "sk_types.h"
 
 SK_C_PLUS_PLUS_BEGIN_GUARD
 
-sk_data_t* sk_data_new_empty();
-sk_data_t* sk_data_new_with_copy(const void* src, size_t length);
-sk_data_t* sk_data_new_from_malloc(const void* memory, size_t length);
-sk_data_t* sk_data_new_subset(const sk_data_t* src, size_t offset, size_t length);
+SK_API sk_data_t* sk_data_new_empty();
+SK_API sk_data_t* sk_data_new_with_copy(const void* src, size_t length);
+SK_API sk_data_t* sk_data_new_from_malloc(const void* memory, size_t length);
+SK_API sk_data_t* sk_data_new_subset(const sk_data_t* src, size_t offset, size_t length);
 
-void sk_data_ref(const sk_data_t*);
-void sk_data_unref(const sk_data_t*);
+SK_API void sk_data_ref(const sk_data_t*);
+SK_API void sk_data_unref(const sk_data_t*);
 
-size_t sk_data_get_size(const sk_data_t*);
-const void* sk_data_get_data(const sk_data_t*);
+SK_API size_t sk_data_get_size(const sk_data_t*);
+SK_API const void* sk_data_get_data(const sk_data_t*);
 
 SK_C_PLUS_PLUS_END_GUARD
 
 #endif