Example fixes (#96)

* Add example for kafka buffered producer

* Add notes regarding bool returned in produce failure callback

* Fix example names

examples/consumer_example.cpp

@@ -0,0 +1,104 @@
+#include <stdexcept>
+#include <iostream>
+#include <csignal>
+#include <boost/program_options.hpp>
+#include "cppkafka/consumer.h"
+#include "cppkafka/configuration.h"
+
+using std::string;
+using std::exception;
+using std::cout;
+using std::endl;
+
+using cppkafka::Consumer;
+using cppkafka::Configuration;
+using cppkafka::Message;
+using cppkafka::TopicPartitionList;
+
+namespace po = boost::program_options;
+
+bool running = true;
+
+int main(int argc, char* argv[]) {
+    string brokers;
+    string topic_name;
+    string group_id;
+
+    po::options_description options("Options");
+    options.add_options()
+        ("help,h",     "produce this help message")
+        ("brokers,b",  po::value<string>(&brokers)->required(), 
+                       "the kafka broker list")
+        ("topic,t",    po::value<string>(&topic_name)->required(),
+                       "the topic in which to write to")
+        ("group-id,g", po::value<string>(&group_id)->required(),
+                       "the consumer group id")
+        ;
+
+    po::variables_map vm;
+
+    try {
+        po::store(po::command_line_parser(argc, argv).options(options).run(), vm);
+        po::notify(vm);
+    }
+    catch (exception& ex) {
+        cout << "Error parsing options: " << ex.what() << endl;
+        cout << endl;
+        cout << options << endl;
+        return 1;
+    }
+
+    // Stop processing on SIGINT
+    signal(SIGINT, [](int) { running = false; });
+
+    // Construct the configuration
+    Configuration config = {
+        { "metadata.broker.list", brokers },
+        { "group.id", group_id },
+        // Disable auto commit
+        { "enable.auto.commit", false }
+    };
+
+    // Create the consumer
+    Consumer consumer(config);
+
+    // Print the assigned partitions on assignment
+    consumer.set_assignment_callback([](const TopicPartitionList& partitions) {
+        cout << "Got assigned: " << partitions << endl;
+    });
+
+    // Print the revoked partitions on revocation
+    consumer.set_revocation_callback([](const TopicPartitionList& partitions) {
+        cout << "Got revoked: " << partitions << endl;
+    });
+
+    // Subscribe to the topic
+    consumer.subscribe({ topic_name });
+
+    cout << "Consuming messages from topic " << topic_name << endl;
+
+    // Now read lines and write them into kafka
+    while (running) {
+        // Try to consume a message
+        Message msg = consumer.poll();
+        if (msg) {
+            // If we managed to get a message
+            if (msg.get_error()) {
+                // Ignore EOF notifications from rdkafka
+                if (!msg.is_eof()) {
+                    cout << "[+] Received error notification: " << msg.get_error() << endl;
+                }
+            }
+            else {
+                // Print the key (if any)
+                if (msg.get_key()) {
+                    cout << msg.get_key() << " -> ";
+                }
+                // Print the payload
+                cout << msg.get_payload() << endl;
+                // Now commit the message
+                consumer.commit(msg);
+            }
+        }
+    }
+}