Add tiny snippets of content to import fixtures.
Remove underscore from ad-hoc files config property. Makes programmatic config less hairy.
Extract updateFileData() method to allow optional LessWorker fileData config.
LessWorker emits 'cleanup' when destroyed, which allows ClusterWorker to detach process.message handler.
Move LessWorker.start() into ClusterWorker, where it actually makes sense.
Refactor LessWorker.build into utility method shared with subclass, allowing disparate signatures.