Added very basic koans for integers

lib/koans/16_integers.ex

@@ -0,0 +1,37 @@
+defmodule Integers do
+  require Integer
+  use Koans
+
+  @intro "Integers"
+
+  koan "Are you odd?" do
+    assert Integer.is_odd(3) == ___
+  end
+
+  koan "Actually you might be even" do
+    assert Integer.is_even(4) == ___
+  end
+
+  koan "Let's grab the individual digits in a list" do 
+    individual_digits = Integer.digits(58127)
+    assert individual_digits == ___
+  end
+
+  koan "Oh no! I need it back together" do 
+    number = Integer.undigits([1, 2, 3, 4])
+
+    assert number == ___
+  end
+
+  koan "I think I need my number as a char" do 
+    char_digit = Integer.to_char_list(7)
+
+    assert char_digit == ___
+  end
+
+  koan "Actually I want my number as a string" do 
+    string_digit = Integer.to_string(1234)
+
+    assert string_digit == ___
+  end
+end