Adapt sage field parameter generation script to optionally output CPP code

[ValarDragon]

To remove some of the boiler plate of adding new field, we should add method/parameter to Antoine's field parameter generation script to directly output the cpp code needed for it.

Antoine's script: https://github.com/scipr-lab/libff/blob/52d77c3ee213b0f1fb49402374f1cf099bb972dd/libff/algebra/curves/params_generator.sage