Move constants and utils to package, apply small fixes

constants/constants.go

@@ -0,0 +1,26 @@
+package constants
+
+import (
+	"github.com/iden3/go-iden3-crypto/utils"
+	"math/big"
+)
+
+// Q is the order of the integer field (Zq) that fits inside the SNARK.
+var Q *big.Int
+
+// Zero is 0.
+var Zero *big.Int
+
+// One is 1.
+var One *big.Int
+
+// MinusOne is -1.
+var MinusOne *big.Int
+
+func init() {
+	Zero = big.NewInt(0)
+	One = big.NewInt(1)
+	MinusOne = big.NewInt(-1)
+	Q = utils.NewIntFromString(
+		"21888242871839275222246405745257275088548364400416034343698204186575808495617")
+}