Add options to monitor or link spawned processes

The following functions are now available for spawning workers
(Task_Type is an atom that is registered with spawn options when
cxy_ctl is initialized):

 execute_task(Task_Type, Mod, Fun, Args)       -> ok.
 maybe_execute_task(Task_Type, Mod, Fun, Args) -> ok | {max_pids, Max}.

   Tasks are spawned processes which return no indication of
   whether they succeeded or not.

 execute_pid_link(Task_Type, Mod, Fun, Args)       -> pid() | {inline, Result}.
 maybe_execute_pid_link(Task_Type, Mod, Fun, Args) -> pid() | {max_pids, Max}.

    The pid_link functions return the pid reference but also link
    the caller so that a crash will take down the caller.

 execute_pid_monitor(Task_Type, Mod, Fun, Args)
          -> {pid(), reference()} | {inline, any()}
 maybe_execute_pid_monitor(Task_Type, Mod, Fun, Args)
          -> {pid(), reference()} | {max_pids, Max}

    The pid_monitor functions return a pid and monitor so that the
    caller can receive 'DOWN' messages.