Export xDir, Direction module
Export Deform from 3D
Remove law-breaking AffineSpace instance

Direction R2 is not actually an AffineSpace.
for all Directions d, d .+^ fullTurn = d
therefore (d .+^ a) .-. d is not a for a >= fullTurn
angleBetweenDirs and rotate give nearly the same behavior
add atan2A function
atDirection is no longer specific to R2
revise arc functions to respect sign of Angle
glue circle into a Loop
add Transformable instance for Direction
Add UndecidableInstances pragma to Direction
Generalize Angle to Angle v and Angle Double
Checkpoint
Checkpoint (non-compiling)