refine the code, more abstract now

1. add new directory algo/ to store algorithms
2. add new directory log/ to store logs
3. require to define the following variables.
   (could be defined in config file or in the bot code)
      $this->config['base_coin'] = 'BTC';
      $this->config['target_coin'] = 'DRK';
4. old_bot/ directory to store the dated bots

Signed-off-by: AceLan Kao <acelan@acelan.idv.tw>