Add draft for Screen module.

src/screen.ml

@@ -0,0 +1,19 @@
+type pixel = {
+  r : char;
+  g : char;
+  b : char;
+  a : char;
+}
+
+type t = {
+  width  : int;
+  height : int;
+  data   : pixel array;
+}
+
+let init_screen w h =
+  {
+    width = w;
+    height = h;
+    data = Array.make_matrix h w { r = 255; g = 255; b = 255; a = 255 }
+  }