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

05_hash_tables/ES6/01_price_of_groceries.js

@@ -0,0 +1,8 @@
+const book = {};
+// an apple costs 67 cents
+book.apple = 0.67;
+// milk costs $1.49
+book.milk = 1.49;
+book.avokado = 1.49;
+
+console.log(book); // { apple: 0.67, milk: 1.49, avocado: 1.49 }

05_hash_tables/ES6/02_check_voter.js

@@ -0,0 +1,14 @@
+const voted = {};
+const checkVoter = (name) => {
+  if (voted[name]) {
+    console.log('kick them out!');
+  } else {
+    voted[name] = true;
+    console.log('let them vote!');
+  }
+};
+
+
+checkVoter('tom'); // let them vote!
+checkVoter('mike'); // let them vote!
+checkVoter('mike'); // kick them out!