Simplify example. Fixes #29. (#30)

Use the Response constructor as a swiss-army knife stream converter to
make the first example much more concise.

Author: jakearchibald

explainer.md

@@ -93,31 +93,13 @@ there are a number of benefits to a built-in capability:
 const compressedReadableStream = inputReadableStream.pipeThrough(new CompressionStream('gzip'));
 ```
 
-### Deflate-compress an ArrayBuffer to a Uint8Array
+### Deflate-compress an ArrayBuffer
 
 ```javascript
-async function compressArrayBuffer(input) {
-  const cs = new CompressionStream('deflate');
-  const writer = cs.writable.getWriter();
-  writer.write(input);
-  writer.close();
-  const output = [];
-  const reader = cs.readable.getReader();
-  let totalSize = 0;
-  while (true) {
-    const { value, done } = await reader.read();
-    if (done)
-      break;
-    output.push(value);
-    totalSize += value.byteLength;
-  }
-  const concatenated = new Uint8Array(totalSize);
-  let offset = 0;
-  for (const array of output) {
-    concatenated.set(array, offset);
-    offset += array.byteLength;
-  }
-  return concatenated;
+function compressArrayBuffer(input) {
+  const stream = new Response(input).body
+    .pipeThrough(new CompressionStream('deflate'));
+  return new Response(stream).arrayBuffer();
 }
 ```