MoveSprite() repositions a Simple Sprite.  After this function is called,
the Simple Sprite is moved to a new position relative to the upper left
corner of the ViewPort.  It is called as follows:

    struct ViewPort     *vp;
    struct SimpleSprite *sprite;
    SHORT               x, y;

    MoveSprite(vp, sprite, x, y);

There are three inputs to MoveSprite().  Set the vp argument to the
address of the ViewPort with which this Simple Sprite interacts or 0 if
this Simple Sprite's position is relative only to the current View.  Set
sprite to the address of your SimpleSprite data structure.  The x and y
arguments sepcify a pixel position to which the Simple Sprite is to be
moved.