Performs point addition on the Baby Jubjub elliptic curve,
calculating a third point from two given points.
Let P1 = (x1, y1) and P2 = (x2, y2) be two arbitrary points of the curve.
Then P1 + P2 = (x3, y3) is calculated in the following way:
x3 = (x1y2 + y1x2)/(1 + dx1x2y1y2)
y3 = (y1y2 - ax1x2)/(1 - dx1x2y1*y2)

Performs point addition on the Baby Jubjub elliptic curve, calculating a third point from two given points. Let P1 = (x1, y1) and P2 = (x2, y2) be two arbitrary points of the curve. Then P1 + P2 = (x3, y3) is calculated in the following way: x3 = (x1

y2 + y1x2)/(1 + dx1x2y1y2) y3 = (y1y2 - ax1x2)/(1 - dx1x2y1*y2)