Adding Scala examples for Chapter 4 and Chapter 5 (#30)

* Add files via upload

* Update 01_countdown.scala

* Update 02_greet.scala

* Update 02_greet.scala

* Create scala

* Delete scala

* Add files via upload

* Add files via upload

05_hash_tables/scala/01_price_of_groceries.scala

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+import scala.collection.mutable
+val book = mutable.Map[String, Double]()
+book += ("apple" -> 0.67)
+book += ("milk" -> 1.49)
+book += ("avocado" -> 1.49)
+println(book)

05_hash_tables/scala/02_check_voter.scala

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+import scala.collection.mutable
+val voted = mutable.Map[String, Boolean]()
+def check_voter(name: String): Unit = {
+  if(voted.exists(_ == (name,true))){
+    println("kick them out!")
+  } else{
+    voted += (name -> true)
+  }
+}
+check_voter("tom")
+check_voter("mike")
+check_voter("mike")