Processor group support

[mwalcott3]

Made threadpool group aware and added support for return values by returning a future when adding a task.

This is needed to utilize all cores on windows systems with more than 64 virtual cores.

https://bitsum.com/general/the-64-core-threshold-processor-groups-and-windows/ https://www.anandtech.com/show/15483/amd-threadripper-3990x-review/3

[stephenberry]

Thanks so much for this!