Web Worker support

[futurist]

Want to use this lib in a WebWorker, but there's a line using window object, which is not exists in WebWorker.

[slavslavov]

I would like to vote for this too. I am trying to use it in QuickJS but have the same issue.

 ./qjs -I msgpack.min.js 
ReferenceError: 'window' is not defined
    at <anonymous> (msgpack.min.js)
    at <eval> (msgpack.min.js)

[ygoe]

I know nothing about web workers, but you might need to adjust the end of the file, where it exports the functions, to your needs. Feel free to create a PR, although I'd need to accept it blindly because I'm not using web workers anywhere.