Add PDF writer.

src/image/PngWriter.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <memory>
+#include <string>
+
+class Image;
+
+class PngWriter
+{
+public:
+    static std::unique_ptr<PngWriter> Create();
+
+    void SetPath(const std::string& path);
+
+    void Write(const std::unique_ptr<Image>& image) const;
+
+private:
+
+    std::string mPath;
+};
+
+using PngWriterPtr = std::unique_ptr<PngWriter>;