Web Worker support?

[cleversprocket]

First I want to say thank you for this project!

I was hoping to use it in a web worker to move image processing off of the main thread. However, when new Vips() is instantiated a ReferenceError: window is not defined is thrown because window is not available to workers. It looks to be coming from emscripten.

Any ideas on how to compile for a worker?

[cleversprocket]

I see now why it is failing, it's because this package instantiates a web worker and I cannot call it from within a worker.

[kleisauke]

For further readers; I think this should work without issues. See: #15 (comment).