Implement CLI usage feature

lib/producer/core/cli.rb

@@ -0,0 +1,27 @@
+module Producer
+  module Core
+    class CLI
+      attr_reader :arguments
+
+      USAGE = "Usage: #{File.basename $0} host recipe_file"
+
+      def initialize(arguments, stdout = $stdout)
+        @stdout     = stdout
+        @arguments  = arguments
+      end
+
+      def run!
+        print_usage_and_exit(64) unless @arguments.length == 2
+      end
+
+
+      private
+
+      def print_usage_and_exit(status)
+        @stdout.puts USAGE
+
+        exit status
+      end
+    end
+  end
+end