Limit Workers to max. avail. CPUs

[kurtextrem]

Fixes #10

[nitish24p]

Each IMageWorker component will now spawn 4 worker threads. As we've removed the worker.terminate call, will those threads still be active when a componentWillUnMount gets called?

[nitish24p]

can you run npm run eslint to see the lint errors and fix those

[kurtextrem]

@nitish24p I fixed the mistakes, sorry for those, I was in a hurry.

[kurtextrem]

There's a big flaw in my current implementation: .onmessage can only exist once it seems. Which means currently ever new instance of ImageWorker replaces the callback function. ~~This means we need something like a Observer pattern.~~

Edit: I've overlooked, that Workers have the .addEventListener interface too, so that's not a problem anymore.