Kill opens the pidfile at the specified path, attempts to read the PID and
kill the process represented by that PID. If the file doesn't exist, the
corresponding process doesn't exist, or the process is successfully killed,
returns nil. Otherwise, returns an error indicating the failure to kill the
process.
On success, deletes the pidfile from the filesystem. Otherwise, leaves it
in place.
Remove deletes the pidfile at the specified path. This does not clean up
the corresponding process, so should only be used when it is known that the
PID contained in the file at the specified path is no longer running.