feat: add helpers.h header for function prototype

Author: harshsankhla18

helpers.h

@@ -0,0 +1,13 @@
+#include "bmp.h"
+
+// Convert image to grayscale
+void grayscale(int height, int width, RGBTRIPLE image[height][width]);
+
+// Convert image to sepia
+void sepia(int height, int width, RGBTRIPLE image[height][width]);
+
+// Reflect image horizontally
+void reflect(int height, int width, RGBTRIPLE image[height][width]);
+
+// Blur image
+void blur(int height, int width, RGBTRIPLE image[height][width]);