Add option to cleanup directory if size threshold exceeded

In response to [this thread](https://communities.sas.com/t5/Administration-and-Deployment/Kill-process/td-p/550461/jump-to/first-unread-message) / scenario. Will implement simple directory deletion and let process terminate as a result rather than killing processes, for safety - i.e. need to add a $CLEANLIMIT [here](https://github.com/Boemska/worktop/blob/master/worktop#L448) and implement relevant cmdline params.