Implement recipe arguments

CLI will stop arguments processing after the special `--' argument,
the rest will be saved in the env and accessible through a new task
keyword: `recipe_argv'.

features/task/recipe_argv.feature

@@ -0,0 +1,13 @@
+Feature: `recipe_argv' task keyword
+
+  Background:
+    Given a recipe with:
+      """
+      task :echo_arguments do
+        echo recipe_argv
+      end
+      """
+
+  Scenario: returns recipe arguments
+    When I successfully execute the recipe with arguments "foo bar"
+    Then the output must contain exactly "foo\nbar\n"