Add async-client support; refine http message dump format.

example/http/client/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_executable(http_client main.cc)
+
+target_link_libraries(http_client webcc ${Boost_LIBRARIES})
+target_link_libraries(http_client "${CMAKE_THREAD_LIBS_INIT}")

example/http/client/main.cc

@@ -0,0 +1,38 @@
+#include <iostream>
+
+#include "webcc/logger.h"
+#include "webcc/http_client.h"
+
+// In order to test this client, create a file index.html whose content is
+// simply "Hello, World!", then start a HTTP server with Python 3:
+//     $ python -m http.server
+// The default port number should be 8000.
+
+void Test() {
+  webcc::HttpRequest request;
+
+  request.set_method(webcc::kHttpGet);
+  request.set_url("/index.html");
+  request.SetHost("localhost", "8000");
+
+  request.Build();
+
+  webcc::HttpResponse response;
+
+  webcc::HttpClient client;
+  if (!client.Request(request)) {
+    return;
+  }
+
+  std::cout << response.content() << std::endl;
+}
+
+int main() {
+  LOG_INIT(webcc::ERRO, 0);
+
+  Test();
+  Test();
+  Test();
+
+  return 0;
+}