Cleanup how koan modules get their intros

lib/koans.ex

@@ -82,11 +82,32 @@ defmodule Koans do
   end
 
   defmacro __before_compile__(env) do
-    koans = Module.get_attribute(env.module, :koans) |> Enum.reverse
+    koans = koans(env)
+    intro = extract_into(env)
     quote do
       def all_koans do
         unquote(koans)
       end
+
+      def intro do
+        unquote(intro)
+      end
     end
   end
+
+  defp koans(env) do
+    env.module
+    |> Module.get_attribute(:koans)
+    |> Enum.reverse
+  end
+
+  defp extract_into(env) do
+    env.module
+    |> Module.get_attribute(:intro)
+    |> default("")
+    |> String.strip
+  end
+
+  defp default(nil, n), do: n
+  defp default(n, _), do: n
 end

test/executor_test.exs

@@ -8,6 +8,10 @@ defmodule ExecuteTest do
   test "stops at the first failing koan" do
     {:failed, %{file: file, line: line}, SampleKoan, _name} = Execute.run_module(SampleKoan)
     assert file == 'test/support/sample_koan.ex'
-    assert line == 4
+    assert line == 8
+  end
+
+  test "can access intro" do
+    assert SampleKoan.intro == "There is something"
   end
 end

test/support/sample_koan.ex

@@ -1,6 +1,10 @@
 defmodule SampleKoan do
   use Koans
 
+  @intro """
+  There is something
+  """
+
   koan "Thinking more than once" do
     assert 3 == ___
     assert 4 == ___