feat: 초기 프로젝트 설정 및 룰.md 파일 추가

api.hyungi.net/node_modules/validator/es/lib/isLuhnNumber.js

@@ -0,0 +1,25 @@
+import assertString from './util/assertString';
+export default function isLuhnNumber(str) {
+  assertString(str);
+  var sanitized = str.replace(/[- ]+/g, '');
+  var sum = 0;
+  var digit;
+  var tmpNum;
+  var shouldDouble;
+  for (var i = sanitized.length - 1; i >= 0; i--) {
+    digit = sanitized.substring(i, i + 1);
+    tmpNum = parseInt(digit, 10);
+    if (shouldDouble) {
+      tmpNum *= 2;
+      if (tmpNum >= 10) {
+        sum += tmpNum % 10 + 1;
+      } else {
+        sum += tmpNum;
+      }
+    } else {
+      sum += tmpNum;
+    }
+    shouldDouble = !shouldDouble;
+  }
+  return !!(sum % 10 === 0 ? sanitized : false);
+}