Add examples

include/cppkafka/buffer.h

@@ -92,6 +92,11 @@ public:
      */
     size_t get_size() const;
 
+    /**
+     * Checks whether this is a non empty buffer
+     */
+    explicit operator bool() const;
+
     /**
      * Converts the contents of the buffer into a string
      */

include/cppkafka/message.h

@@ -84,6 +84,11 @@ public:
      */
     rd_kafka_resp_err_t get_error() const;
 
+    /**
+     * Gets the error as a string
+     */
+    std::string get_error_string() const;    
+
     /**
      * Gets the topic that this message belongs to
      */