add drawCircle to c api

include/c/sk_canvas.h

Index: include/c/sk_canvas.h
diff --git a/include/c/sk_canvas.h b/include/c/sk_canvas.h
index f6c0d4e1c143f34cf1906dd46c1ce761931c1368..1e1dd24f998ef40a5e1dd07357b8acd9014c3eba 100644
--- a/include/c/sk_canvas.h
+++ b/include/c/sk_canvas.h
@@ -103,6 +103,11 @@ SK_API void sk_canvas_draw_paint(sk_canvas_t*, const sk_paint_t*);
 */
 SK_API void sk_canvas_draw_rect(sk_canvas_t*, const sk_rect_t*, const sk_paint_t*);
 /**
+ *  Draw the circle centered at (cx, cy) with radius rad using the specified paint.
+ *  The circle will be filled or framed based on the style in the paint
+ */
+SK_API void sk_canvas_draw_circle(sk_canvas_t*, float cx, float cy, float rad, const sk_paint_t*);
+/**
     Draw the specified oval using the specified paint. The oval will be
     filled or framed based on the style in the paint
 */