EdDSA gadget

[yelhousni]

Reduce the number of constraints of a single EdDSA verification (e.g. Groth16/BN254 -2049 constraints).

[yelhousni]

Modulo Lookup2 for fixed inputs in PLONK #254

[ThomasPiellard]

So the error was not the lookup table but a wrong op in the sparse_r1cs constraint system:
r.ModInverse(&r, q).Mul(&l, &r).Mod(&l, q) instead of
r.ModInverse(&r, q).Mul(&l, &r).Mod(&r, q)

[gbotrel]

@yelhousni still a draft?

[yelhousni]

@yelhousni still a draft?

PR is ready after Thomas' fix.