Cleanup how koan modules get their intros

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 == ___