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

src/c/sk_surface.cpp

Index: src/c/sk_surface.cpp
diff --git a/src/c/sk_surface.cpp b/src/c/sk_surface.cpp
index 722ca46a2f92f31f8db82bf7cba0fbc26d94629c..b8fbc63f63f4200457b28c8a8262dd320b0aae2b 100644
--- a/src/c/sk_surface.cpp
+++ b/src/c/sk_surface.cpp
@@ -5,14 +5,6 @@
  * found in the LICENSE file.
  */
 
-#include "sk_canvas.h"
-#include "sk_data.h"
-#include "sk_image.h"
-#include "sk_paint.h"
-#include "sk_path.h"
-#include "sk_surface.h"
-#include "sk_types_priv.h"
-
 #include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImage.h"
@@ -23,6 +15,14 @@
 #include "SkPictureRecorder.h"
 #include "SkSurface.h"
 
+#include "sk_canvas.h"
+#include "sk_data.h"
+#include "sk_image.h"
+#include "sk_paint.h"
+#include "sk_path.h"
+#include "sk_surface.h"
+#include "sk_types_priv.h"
+
 const struct {
     sk_colortype_t  fC;
     SkColorType     fSK;