Two workers & worker termination (#198)

* Refactoring codecs

* Plugging in new processor

* Fixing decorator

* MozJPEG free issue

* Better worker aborting, and terminate workers that aren't used for 10 seconds

* Better comment

* Ooops, half-typed comment

* Uncommenting problematic line

* Surma fixed it!

* Abstracting WASM initialisation

* Better comment

* Don't need this.

* Adding ticket

* noInitalRun

* Reverting MozJPEG issue demo

* Making a const for worker timeout

* Inline docs

* Bail early rather than nesting

* Addressing nits

src/codecs/imagequant/processor.ts

@@ -0,0 +1,21 @@
+import imagequant, { QuantizerModule } from '../../../codecs/imagequant/imagequant';
+import wasmUrl from '../../../codecs/imagequant/imagequant.wasm';
+import { QuantizeOptions } from './processor-meta';
+import { initWasmModule } from '../util';
+
+let emscriptenModule: Promise<QuantizerModule>;
+
+export async function process(data: ImageData, opts: QuantizeOptions): Promise<ImageData> {
+  if (!emscriptenModule) emscriptenModule = initWasmModule(imagequant, wasmUrl);
+
+  const module = await emscriptenModule;
+
+  const result = opts.zx ?
+      module.zx_quantize(data.data, data.width, data.height, opts.dither)
+    :
+      module.quantize(data.data, data.width, data.height, opts.maxNumColors, opts.dither);
+
+  module.free_result();
+
+  return new ImageData(new Uint8ClampedArray(result.buffer), result.width, result.height);
+}