add abs function to Math library

Author: ItsNickBarry

contracts/utils/Math.sol

@@ -3,6 +3,15 @@
 pragma solidity ^0.8.8;
 
 library Math {
+    /**
+     * @notice calculate the absolute value of a number
+     * @param a number whose absoluve value to calculate
+     * @return absolute value
+     */
+    function abs(int256 a) internal pure returns (uint256) {
+        return uint256(a < 0 ? -a : a);
+    }
+
     /**
      * @notice select the greater of two numbers
      * @param a first number

contracts/utils/MathMock.sol

@@ -7,6 +7,10 @@ import { Math } from './Math.sol';
 contract MathMock {
     using Math for uint256;
 
+    function abs(int256 a) external pure returns (uint256) {
+        return Math.abs(a);
+    }
+
     function max(uint256 a, uint256 b) external pure returns (uint256) {
         return Math.max(a, b);
     }

test/utils/Math.ts

@@ -11,6 +11,14 @@ describe('Math', function () {
   });
 
   describe('__internal', function () {
+    describe('#abs(int256)', function () {
+      it('returns the absolute value of a number', async () => {
+        expect(await instance.callStatic.abs(-1)).to.equal(1);
+        expect(await instance.callStatic.abs(0)).to.equal(0);
+        expect(await instance.callStatic.abs(1)).to.equal(1);
+      });
+    });
+
     describe('#max(uint256,uint256)', function () {
       it('returns the greater of two numbers', async () => {
         expect(