Implement set' and get' recipe keywords:

`set' registers a value at given index in env registry, `get'
retrieves a value at given index.

features/recipes/registry.feature

@@ -0,0 +1,21 @@
+Feature: key/value registry
+
+  Scenario: `set' keyword registers a value in the registry
+    Given a recipe with:
+      """
+      set :some_key, 'some_value'
+
+      puts env.registry[:some_key]
+      """
+    When I successfully execute the recipe
+    Then the output must contain "some_value"
+
+  Scenario: `get' keyword fetches a value from the registry
+    Given a recipe with:
+      """
+      set :some_key, 'some_value'
+
+      puts get :some_key
+      """
+    When I successfully execute the recipe
+    Then the output must contain "some_value"

lib/producer/core/recipe/dsl.rb

@@ -37,6 +37,14 @@ module Producer
             task("#{name}", *args, &block)
           end
         end
+
+        def set(key, value)
+          env[key] = value
+        end
+
+        def get(key)
+          env[key]
+        end
       end
     end
   end

spec/producer/core/recipe/dsl_spec.rb

@@ -100,5 +100,19 @@ module Producer::Core
         end
       end
     end
+
+    describe '#set' do
+      it 'registers a key/value pair in env registry' do
+        dsl.set :some_key, :some_value
+        expect(env[:some_key]).to eq :some_value
+      end
+    end
+
+    describe '#get' do
+      it 'fetches a value from the registry at given index' do
+        dsl.set :some_key, :some_value
+        expect(dsl.get :some_key).to eq :some_value
+      end
+    end
   end
 end