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.