Reorganize the repo structure (#2503)

Co-authored-by: Francisco Giordano <frangio.1@gmail.com>

contracts/utils/math/Math.sol

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Standard math utilities missing in the Solidity language.
+ */
+library Math {
+    /**
+     * @dev Returns the largest of two numbers.
+     */
+    function max(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a >= b ? a : b;
+    }
+
+    /**
+     * @dev Returns the smallest of two numbers.
+     */
+    function min(uint256 a, uint256 b) internal pure returns (uint256) {
+        return a < b ? a : b;
+    }
+
+    /**
+     * @dev Returns the average of two numbers. The result is rounded towards
+     * zero.
+     */
+    function average(uint256 a, uint256 b) internal pure returns (uint256) {
+        // (a + b) / 2 can overflow, so we distribute
+        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
+    }
+}