Header support implementation (#115)

* header support implementation

* Fixed issue when ptr is null and doesn't have a cloner function

* Code complete with test cases

updated travis file with v0.11.5

* Added compile time check for rdkafka header support version

* Changes per last code review

* Using brace list initializers

include/cppkafka/producer.h

@@ -113,6 +113,7 @@ public:
      * \param builder The builder class used to compose a message
      */
     void produce(const MessageBuilder& builder);
+    void produce(MessageBuilder&& builder);
     
     /**
      * \brief Produces a message
@@ -120,6 +121,7 @@ public:
      * \param message The message to be produced
      */
     void produce(const Message& message);
+    void produce(Message&& message);
 
     /**
      * \brief Polls on this handle
@@ -157,6 +159,15 @@ public:
      */
     void flush(std::chrono::milliseconds timeout);
 private:
+#if (RD_KAFKA_VERSION >= RD_KAFKA_HEADERS_SUPPORT_VERSION)
+    void do_produce(const MessageBuilder& builder, MessageBuilder::HeaderListType&& headers);
+    void do_produce(const Message& message, MessageBuilder::HeaderListType&& headers);
+#else
+    void do_produce(const MessageBuilder& builder);
+    void do_produce(const Message& message);
+#endif
+    
+    // Members
     PayloadPolicy message_payload_policy_;
 };