Implement `file_append' task action

lib/producer/core/actions/file_append.rb

@@ -0,0 +1,23 @@
+module Producer
+  module Core
+    module Actions
+      class FileAppend < Action
+        def apply
+          fs.file_write path, combined_content
+        end
+
+        def path
+          arguments[0]
+        end
+
+        def content
+          arguments[1]
+        end
+
+        def combined_content
+          fs.file_read(path) + content
+        end
+      end
+    end
+  end
+end

lib/producer/core/task/dsl.rb

@@ -13,9 +13,11 @@ module Producer
         define_action :echo,  Actions::Echo
         define_action :sh,    Actions::ShellCommand
 
-        define_action :mkdir,                 Actions::Mkdir
-        define_action :file_write,            Actions::FileWriter
+        define_action :mkdir, Actions::Mkdir
+
+        define_action :file_append,           Actions::FileAppend
         define_action :file_replace_content,  Actions::FileReplaceContent
+        define_action :file_write,            Actions::FileWriter
 
         attr_reader :env, :block, :actions