Add ES6 Examples to all chapters (#38)

* add ES6 example for binary search

* add ES6 example for selection sort

* add ES6 example for countdown

* add ES6 example for greet

* add ES6 example for factorial

* edit ES6 example for quicksort

* add ES6 example for loop sum

* add ES6 example for recursive sum

* add ES6 example for recursive count

* add ES6 example for recursive max

* add ES6 example for price of groceries

* add ES6 example for check voter

* add ES6 example for breadth-first search

* add ES6 example for dijkstras algorithm

* edit ES6 example for dijkstras algorithm

* edit ES6 example for set covering

* add ES6 example for longest common subsequence

01_introduction_to_algorithms/ES6/01_binary_search.js

@@ -0,0 +1,25 @@
+const binarySearch = (list, item) => {
+  let low = 0;
+  let high = list.length - 1;
+
+  while (low <= high) {
+    const mid = Math.floor((low + high) / 2);
+    const guess = list[mid];
+
+    if (guess === item) {
+      return mid;
+    }
+    if (guess > item) {
+      high = mid - 1;
+    } else {
+      low = mid + 1;
+    }
+  }
+
+  return null;
+};
+
+const myList = [1, 3, 5, 7, 9];
+
+console.log(binarySearch(myList, 3)); // 1
+console.log(binarySearch(myList, -1)); // null