Compile and update the examples in the README

examples/multipart_messages.cpp

@@ -0,0 +1,31 @@
+#include <iostream>
+#include <zmq_addon.hpp>
+
+int main()
+{
+    zmq::context_t ctx;
+    zmq::socket_t sock1(ctx, zmq::socket_type::push);
+    zmq::socket_t sock2(ctx, zmq::socket_type::pull);
+    sock1.bind("tcp://127.0.0.1:*");
+    const std::string last_endpoint =
+        sock1.get(zmq::sockopt::last_endpoint);
+    std::cout << "Connecting to "
+              << last_endpoint << std::endl;
+    sock2.connect(last_endpoint);
+
+    std::array<zmq::const_buffer, 2> send_msgs = {
+        zmq::str_buffer("foo"),
+        zmq::str_buffer("bar!")
+    };
+    if (!zmq::send_multipart(sock1, send_msgs))
+        return 1;
+
+    std::vector<zmq::message_t> recv_msgs;
+    const auto ret = zmq::recv_multipart(
+        sock2, std::back_inserter(recv_msgs));
+    if (!ret)
+        return 1;
+    std::cout << "Got " << *ret
+              << " messages" << std::endl;
+    return 0;
+}