export Open/Closed and Offset from Segment, and cleanup
pull out Trail redesign into a separate module

It compiles, but is missing lots of implementations.
Trail: add emptyTrail, openTrail, openTrail'
split out redesigned TrailLike into a separate module
Show, Eq, Ord, V, Transformable, and Enveloped for Trail
D.TrailLike: add (~~) and explodeTrail
D.Path: open/closed redesign