Big update - maybe have ctl point behavior figured out
working but i think y axis is flipped somehow

because y axis is downward I think i have to multiply all y values by -1
before using them to calculate angles. For example, a down-right slope
line calcs to -xx radians for the angle, but actually it is a positive
angle moving positive in x and y direction
Working!!!!!!

Works perfectly.
Next: want to add states but have to think about design.  I think paths
have start and end point (for controlling them). States will have
connections points to snap to. Add hand on hover of line to indicate
line will be translated (moved) not stretched.