Implement task evaluation feature

features/task.feature

@@ -0,0 +1,12 @@
+Feature: tasks
+
+  Scenario: evaluates ruby code grouped in task blocks
+    Given a recipe with:
+      """
+      task :hello do
+        puts 'hello from recipe'
+      end
+      """
+    When I execute the recipe
+    Then the exit status must be 0
+    And the output must contain "hello from recipe"