Adding a remove-old-ipc option to start.

The idea being to allow the naught process to clean up after an erroneous
shutdown, rather than having to manually run a check before starting the
naught process, which is more clumsy and less reliable (to my mind).
Instead this adds a flag to naught which will make it try to unlink an
existing ipc file if an invalid one is found.


I'm not sure whether you'd be keen on this idea, but I think it's quite useful......
Happy to tweak as needed (eg more docs? -- I wasn't sure whether the README is autogenerated of some description, but am happy to transpose the doc changes to there; and would be happy to add a general description for the new argument as well.) I tried my best to match the code style etc, but can change anything as required :-)

ps, thank you for all your awesome work, naught is really awesome :-)