v6.7.0

• Refactored the code, especially in and around the sc-broker module.
• Improved visibility of broker errors (better stack traces).
• Improved visibility of errors throughout SC in general.
• Brokers recover from crashes faster.
• Broker actions and messages now have improved buffering so broker crashes/recovery should be more seamless.
• Improved buffering for all IPC messages: sendToBroker, sendToWorker and sendToMaster...
• Improved tests around brokers.