Handle errors in tests functions as well

This allows failures to be passed back to the parent rather than the
koan process just dying and the parent stuck waiting for the result.

lib/koans.ex

@@ -33,8 +33,12 @@ defmodule Koans do
     single_var = Blanks.replace(body, Macro.var(:answer, Koans))
     quote do
       def unquote(name)(answer) do
-        unquote(single_var)
-        :ok
+        try do
+          unquote(single_var)
+          :ok
+        rescue
+          e in _ -> e
+        end
       end
     end
   end
@@ -44,8 +48,12 @@ defmodule Koans do
     quote do
       def unquote(name)({:multiple, answers}) do
         converted = List.to_tuple(answers)
-        unquote(multi_var)
-        :ok
+        try do
+          unquote(multi_var)
+          :ok
+        rescue
+          e in _ -> e
+        end
       end
     end
   end