Added Schnorr Signature & EC256 libraries (#142)

* init bn254 & schnorr

* fixes & added basic test for schnorr

* small adjustments

* rewrote schnorr for any curve

* adjustments

* refactored

* refactored

* refactored ecdsa

* renamed

* rm unused fn

* added docs

* upd comment

* added tests

* basic fixes

* fix

* fixes

* bumped version

* cov 100

* upd readme

* quick readme fix

---------

Co-authored-by: Artem Chystiakov <artem.ch31@gmail.com>

Author: dovgopoly

README.md

@@ -46,10 +46,12 @@ contracts
 │   ├── bn
 │   │   └── U512 — "A hyperoptimized uint512 implementation"
 │   ├── crypto
-│   │   ├── ECDSA256 — "ECDSA verification over any 256-bit curves"
-│   │   ├── ECDSA384 — "ECDSA verification over any 384-bit curves"
-│   │   ├── ECDSA512 — "ECDSA verification over any 512-bit curves"
-│   │   └── RSASSAPSS — "RSASSA-PSS verification with MGF1"
+│   │   ├── EC256 — "Elliptic curve arithmetic over a 256-bit prime field"
+│   │   ├── ECDSA256 — "ECDSA verification over any 256-bit curve"
+│   │   ├── ECDSA384 — "ECDSA verification over any 384-bit curve"
+│   │   ├── ECDSA512 — "ECDSA verification over any 512-bit curve"
+│   │   ├── Schnorr256 — "Schnorr signature verification over any 256-bit curve"
+│   │   └── RSASSAPSS — "RSASSA-PSS signature verification with MGF1"
 │   ├── data—structures
 │   │   ├── AvlTree — "AVL tree implementation with an iterator traversal"
 │   │   ├── CartesianMerkleTree — "CMT reference implementation"