Adding the rest of files:

- ASM is disabled
- Neug needs full rewrite
- Flash is based on PiMoroni 4MB flash (needs adjust)

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

modp256k1.h

@@ -0,0 +1,9 @@
+extern const bn256 p256k1;
+#define P256K1 (&p256k1)
+
+void modp256k1_add (bn256 *X, const bn256 *A, const bn256 *B);
+void modp256k1_sub (bn256 *X, const bn256 *A, const bn256 *B);
+void modp256k1_reduce (bn256 *X, const bn512 *A);
+void modp256k1_mul (bn256 *X, const bn256 *A, const bn256 *B);
+void modp256k1_sqr (bn256 *X, const bn256 *A);
+void modp256k1_shift (bn256 *X, const bn256 *A, int shift);