Update #inspect for Dimensions and Point

Was: <Shoes::Dimensions:0x000047e4 relative: (10, 20)->(100, 200), \
      absolute: (, )->(, ) 90x180>

Now: (Shoes::Dimensions:0x000047e4 relative:(10,20)->(100,200) \
      absolute:(_,_)->(_,_) 90x180)

Both Point and Dimensions use '_' rather than the empty string for
values that are falsey. This makes it clear that there's an spot there
with nothing in it, rather than looking like a mistake.