Implement `macro' recipe keyword

features/recipes/macro.feature

@@ -0,0 +1,40 @@
+Feature: `macro' recipe keyword
+
+  Scenario: declares new keyword accepting task code
+    Given a recipe with:
+      """
+      macro :hello do
+        echo 'hello macro'
+      end
+
+      hello
+      """
+    When I successfully execute the recipe
+    Then the output must contain "hello macro"
+
+  Scenario: supports arguments
+    Given a recipe with:
+      """
+      macro :my_echo do |kind, message|
+        echo "#{kind}: #{message}"
+      end
+
+      my_echo 'my', 'hello'
+      """
+    When I successfully execute the recipe
+    Then the output must contain "my: hello"
+
+  Scenario: supports arguments in conditions
+    Given a recipe with:
+      """
+      macro :my_echo do |message|
+        condition { message =~ /bar/ }
+
+        echo message
+      end
+
+      %w[foo bar].each { |e| my_echo e }
+      """
+    When I successfully execute the recipe
+    Then the output must not contain "foo"
+    And the output must contain "bar"