worker: Create an rrqueue worker
In traitecoevo/rrqueue: Scalable Job Queues for R with 'Redis'

Create an rrqueue worker. This blocks the main loop.

1 2	worker(queue_name, redis_host = "127.0.0.1", redis_port = 6379, heartbeat_period = 30, heartbeat_expire = 90, key_worker_alive = NULL)

`queue_name`	Queue name
`redis_host`	Host name/IP for the Redis server
`redis_port`	Port for the Redis server
`heartbeat_period`	Period between heartbeat pulses
`heartbeat_expire`	Time that heartbeat pulses will persist for (must be greater than `heartbeat_period`)
`key_worker_alive`	Optional key to write to when the worker becomes alive. The worker will push onto this key so that another process can monitor it and determine when a worker has come up.