Support web workers

[EtaiG]

Sometimes, people want to use the code in web-workers.

Specifically, one of my relatives wanted to use this library in a Wix Corvid application. They need to use a target compiled for web-workers in order for it to work.
This PR creates a worker target.

After the build, it would probably be good to add a link to unpkg with the compiled worker target, to make it easier

[BehindTheMath]

@EtaiG Instead of creating a new Webpack config, would something like this work?

[EtaiG]

@EtaiG Instead of creating a new Webpack config, would something like this work?

Theoretically yes, and it would be a better solution.
I haven't tried any of the workarounds yet, but webpack/webpack#6525 (comment) mentions that they are not enough.