[curves] new 25519 measurements of formally verified implementations

[Jason A. Donenfeld]

Hey Dan,

Thanks for the pointer and the link to the slides. I've heard about
this implementation before, but I was never able to get a hold of the
source to try it out. I just emailed him to see if it's available
somewhere. Looks like there's a conference paper from Latincrypt 2015
that describes its implementation.

Jason