v2.0.0: Multiserver and reconnect support

• Bug fixes (thanks @pyros2097!)
• Convert to readable-stream and isa-stream to eliminate node-version-specific bugs
• Add submitTimeout and resultTimeout
• Add support for multiple gearman servers and automatic reconnection
• Breaking API change: Rename registerWorker to registerWorkerStream, add new registerWorker that reads the payload and puts it on task.payload.