Issue 116 - Document the libadblockplus API

include/AdblockPlus/DefaultLogSystem.h

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 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/>.
  */
 
 #ifndef ADBLOCK_PLUS_DEFAULT_LOG_SYSTEM_H
 #define ADBLOCK_PLUS_DEFAULT_LOG_SYSTEM_H
 
 #include "LogSystem.h"
 
 namespace AdblockPlus
 {
+  /**
+   * `LogSystem` implementation that writes messages to stderr.
+   */
   class DefaultLogSystem : public LogSystem
   {
   public:
     void operator()(LogLevel logLevel, const std::string& message,
           const std::string& source);
   };
 }
 
 #endif