refactor workers to reduce duplication
standardise debug logging of master <-> runner <-> worker activity a bit more - log from the master rather than making an extra network trip to send the log.  rename "next" command to the master to "next_file" as it can now be a straight passthrough from the worker.
show the time in all output messages
implement build burndown reports
implement --split-files option to run the scenarios inside cucumber feature files in parallel