Various feature additions

I figured you might want this bunch of edits.  There's a few features in there:

 * Handling of signals (they are passed through to the child process)
 * Runtime configuration of poll rate
 * Stricter flushing of files when writing output
 * A modification to the hashbang line to facilitate the flushing behaviour above
 * Support for `-h` to show usage info

Thanks!
-- Steve