Bug fix: Error occurs when a relation between same length spans was drawn at the initiation.
Bug fix: A big arrow was rest when a relation has been selected during hover.
Bug fix: Error occurs when a relation between same length spans was drawn at the initiation.
Increase the maximum of the line height to 50.
Cache all span position because an alternating between getting offset and setting offset is slow.
Tuning by using the 'jsPlumbInstance.repaintEverything'.