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/browser-png/encoder-meta.ts

@@ -0,0 +1,8 @@
+export interface EncodeOptions {}
+export interface EncoderState { type: typeof type; options: EncodeOptions; }
+
+export const type = 'browser-png';
+export const label = 'Browser PNG';
+export const mimeType = 'image/png';
+export const extension = 'png';
+export const defaultOptions: EncodeOptions = {};