add: Canvas::Clear method to clear canvas

core/base/Canvas.cpp

@@ -445,6 +445,12 @@ namespace easy2d
 		cache_expired_ = true;
 	}
 
+	void Canvas::Clear()
+	{
+		render_target_->Clear();
+		cache_expired_ = true;
+	}
+
 	spImage Canvas::ExportToImage() const
 	{
 		auto image = new Image(GetBitmap());

core/base/Canvas.h

@@ -153,6 +153,9 @@ namespace easy2d
 		// ¡žśĚîłä
 		void FillPath();
 
+		// 헌왕뺌꼈
+		void Clear();
+
 		// ÉčÖĂĚîłäŃŐÉŤ
 		void SetFillColor(
 			const Color& color