The Montgomery form of the Jubjub curve [ZPS:A.2].
The Jubjub curve\mathbb{J} [ZPS:5.4.9.3] is a twisted Edwards curve.
However, because of the birational equivalence between
Montgomery and twisted Edwards curves, there is also a Montgomery form of Jubjub
\mathbb{M} [ZPS:A.2].
Here we define it, using our general mapping,
and show some properties of it.
This mapping uses a scaling factor,
which ensures that the resulting Montgomery B is 1.
