YadaCoin mutli-processing and fork fix

I've discovered an critical data issue caused by a bug in the code that caused a fork at height 14485. I've release a fix for this bug but it will require all miners to download the latest version of the software to recover from the fork. Unfortunately, those who have won coins after height 14484 will have to mine for those coins again.

I have also included multiprocessing for miners who requested higher CPU utilization.

Big thanks to everyone for the support and enthusiasm as we continue to grow.