GLV/GlS method for Twisted Edwards Curves

[HarryR]

See:

• https://eprint.iacr.org/2010/005.pdf
• https://eprint.iacr.org/2015/421.pdf
• https://koclab.cs.ucsb.edu/teaching/cren/project/2018/BistarkeyRez.pdf
• https://eprint.iacr.org/2015/1114.pdf
• https://www.iacr.org/workshops/ches/ches2013/presentations/CHES2013_Session6_2.pdf

This could potentially speed-up point multiplication by using an 'efficiently computable endomorphism', using the GLV method, by reducing the number of point doublings.