Added several functions of Plucker coordinates.

In particular, more common functions on directed lines are now
implemented: closest point to origin, distance from origin, screw
relationship between two lines, directed and undirected equality.
Cleaned up passes definition.
Don't re-export Plucker from Linear.

New definitions in Linear.Plucker run the risk of colliding with names
in client code. Since Linear.Plucker is perhaps more niche than things
like V3, require users to explicitly import it.