Automatic crosslink of endpoints
Test fixup and cleanup
Remove labels and symbols from test examples
Fix relationship creation
Remove unused perpendicularCoordinate()
Eliminate entity knowledge of its endpoints
Side does not need to set itself on endpoint
Remove entity.removeEndpoint()
Cleanup 2-way dependency in nearestSide()
Move centerOffsetCoordinates() to Entity
Calculate parallelCoordinate() in Endpoint
Endpoint knows its outward vector
Remove orientation property
Move arrowhead methods to Endpoint