Add initial consumer code

include/cppkafka/consumer.h

@@ -0,0 +1,28 @@
+#ifndef CPP_KAFKA_CONSUMER_H
+#define CPP_KAFKA_CONSUMER_H
+
+#include <vector>
+#include <string>
+#include "kafka_handle_base.h"
+#include "topic_partition_list.h"
+
+namespace cppkafka {
+
+class Configuration;
+class TopicConfiguration;
+
+class Consumer : public KafkaHandleBase {
+public:
+    Consumer(const Configuration& config);
+
+    void subscribe(const std::vector<std::string>& topics);
+    void unsubscribe();
+
+    void assign(const TopicPartitionList& topic_partitions);
+private:
+    void check_error(rd_kafka_resp_err_t error);
+};
+
+} // cppkafka
+
+#endif // CPP_KAFKA_CONSUMER_H