Add support for PNG decoding (encoding still buggy)

cli/src/image_data.js

@@ -1,6 +1,11 @@
 export default class ImageData {
   constructor(data, width, height) {
-    this.data = data;
+    // Need to manually copy the memory as wasm-bindgen does not by default
+    // and by the time we get control in JS land, the memory has already
+    // been corrupted.
+    // FIXME: This is bad because it’s overhead that we should only need
+    // to pay for Rust, not for C++.
+    this.data = new Uint8ClampedArray(data);
     this.width = width;
     this.height = height;
   }