Add ability to run as daemon on non-Windows OS's.

Added some code to fork/daemonize the process when -d or --daemon is passed at the command line.

This needs a bit of work still (for example, output should go to a log instead of /dev/null, proper startup/shutdown scripts should be created for the various platforms) but it should make it possible for folks to run on linux-based NAS's, etc. (see #22)