NewCmdRunner returns an implementation of runner.Runner for running a plugin as a subprocess.

ReattachFunc returns a function that allows reattaching to a plugin running as a plain process.

ErrProcessNotFound is returned when a client is instantiated to reattach to an existing process and it isn't found.

CmdAttachedRunner is mostly a subset of CmdRunner, except the Wait function does not assume the process is a child of the host process, and so uses a different implementation to wait on the process.

CmdRunner implements the runner.Runner interface.