Add screen::unpackPNG()

libs/core/shims.d.ts

@@ -70,6 +70,12 @@ declare namespace serial {
     //% shim=serial::writeDmesg
     function writeDmesg(): void;
 }
+declare namespace screen {
+
+    /** Decompresses a 1-bit gray scale PNG image to icon format. */
+    //% shim=screen::unpackPNG
+    function unpackPNG(png: Buffer): Buffer;
+}
 declare namespace screen {
 
     /** Double size of an icon. */