Daemon option for running halibot

[sjrct]

Should be able to run halibot as a daemon (perhaps with a -d, or perhaps as default with a foreground option). We would also need a way to tell what halibot instance is running, perhaps a pid file alongside the main config. Should have a command to stop a running instance and the add and rm commands should act on a running halibot instance if it actually is running. This might perhaps imply that we should move config management into the Halibot instance as implied by #57.

[richteer]

This should probably actually become the default option, allowing the CLI to handle only configuration details and starting/stopping. We should include a local socket-based (or alternative) agent that would allow for communication via CLI when the instance is running.