Support movables in `workerData` option

[aleclarson]

Two feature requests here:

1. Passing workerData: Tinypool.move(data) is not supported, even though new Worker has a transferList option.

2. If workerData is a plain object, Tinypool should iterate its property values to see if any of them are movable, thereby allowing multiple movables to be passed through the workerData option.

[AriPerkkio]

@aleclarson is this feature request still valid? It seems 2 years old by now.