Resume a paused timer, re-activating it.  Subsequent time accumulates in
    the total.

    Returns:
        float: The current time.

    Raises:
        PausedError: If timer was not in paused state.
        StoppedError: If timer was already stopped.

def resume():
    """
    Resume a paused timer, re-activating it.  Subsequent time accumulates in
    the total.

    Returns:
        float: The current time.

    Raises:
        PausedError: If timer was not in paused state.
        StoppedError: If timer was already stopped.
    """
    t = timer()
    if f.t.stopped:
        raise StoppedError("Cannot resume stopped timer.")
    if not f.t.paused:
        raise PausedError("Cannot resume timer that is not paused.")
    f.t.paused = False
    f.t.start_t = t
    f.t.last_t = t
    return t