Rename ErrorCallback into LogSystem, provide a proper console API

src/DefaultLogSystem.cpp

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2013 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <iostream>
-#include <AdblockPlus/DefaultErrorCallback.h>
+#include <AdblockPlus/DefaultLogSystem.h>
 
-void AdblockPlus::DefaultErrorCallback::operator()(const std::string& message)
+void AdblockPlus::DefaultLogSystem::operator()(AdblockPlus::LogSystem::LogLevel logLevel,
+    const std::string& message, const std::string& source)
 {
-  std::cerr << "Error: " << message << std::endl;
+  switch (logLevel)
+  {
+    case TRACE:
+      std::cerr << "Traceback:" << std::endl;
+      break;
+    case LOG:
+      break;
+    case INFO:
+      std::cerr << "Info: ";
+      break;
+    case WARN:
+      std::cerr << "Warning: ";
+      break;
+    case ERROR:
+      std::cerr << "Error: ";
+      break;
+  }
+  std::cerr << message;
+  if (source.size())
+    std::cerr << " at " << source;
+  std::cerr << std::endl;
 }