refactoring the beansdb's proxy

1. accept INT signal to re-open new accesslog and new errorlog for a better rotating.
2. use yaml format as the configuration file.
3. use semi-auto/semi-manual configuration to specified node->bucket mapping relationship.
4. some bugfixing.
5. optimizing memory usage, and cpu usage. 
6. support read only mode while just using get/get_multi command.
7. ...