Fix windows linker errors (#120)

include/cppkafka/message_internal.h

@@ -31,6 +31,7 @@
 #define CPPKAFKA_MESSAGE_INTERNAL_H
 
 #include <memory>
+#include "macros.h"
 
 namespace cppkafka {
 
@@ -45,7 +46,7 @@ using InternalPtr = std::shared_ptr<Internal>;
 /**
  * \brief Private message data structure
  */
-class MessageInternal {
+class CPPKAFKA_API MessageInternal {
 public:
     MessageInternal(void* user_data, std::shared_ptr<Internal> internal);
     static std::unique_ptr<MessageInternal> load(Message& message);

include/cppkafka/utils/backoff_committer.h

@@ -37,6 +37,7 @@
 #include "../consumer.h"
 #include "backoff_performer.h"
 #include "../detail/callback_invoker.h"
+#include "../macros.h"
 
 namespace cppkafka {
 
@@ -71,7 +72,7 @@ namespace cppkafka {
  * committer.commit(some_message);
  * \endcode
  */
-class BackoffCommitter : public BackoffPerformer {
+class CPPKAFKA_API BackoffCommitter : public BackoffPerformer {
 public:
     /**
      * \brief The error callback.

include/cppkafka/utils/compacted_topic_processor.h

@@ -37,6 +37,7 @@
 #include <boost/optional.hpp>
 #include "../buffer.h"
 #include "../consumer.h"
+#include "../macros.h"
 
 namespace cppkafka {
 /**
@@ -110,7 +111,7 @@ private:
 };
 
 template <typename Key, typename Value>
-class CompactedTopicProcessor {
+class CPPKAFKA_API CompactedTopicProcessor {
 public:
     /**
      * The type of events generated by this processor

include/cppkafka/utils/poll_strategy_base.h

@@ -35,6 +35,7 @@
 #include "../queue.h"
 #include "../topic_partition_list.h"
 #include "poll_interface.h"
+#include "../macros.h"
 
 namespace cppkafka {
 
@@ -52,7 +53,7 @@ struct QueueData {
  *
  * \brief Base implementation of  the PollInterface
  */
-class PollStrategyBase : public PollInterface {
+class CPPKAFKA_API PollStrategyBase : public PollInterface {
 public:
     using QueueMap = std::map<TopicPartition, QueueData>;