Add support for PNG decoding (encoding still buggy)

cli/src/emscripten-utils.js

@@ -1,10 +1,13 @@
-export function instantiateEmscriptenWasm(factory, path) {
+export function pathify(path) {
   if (path.startsWith("file://")) {
     path = path.slice("file://".length);
   }
+  return path;
+}
+export function instantiateEmscriptenWasm(factory, path) {
   return factory({
     locateFile() {
-      return path;
+      return pathify(path);
     }
   });
 }