* 2.2.0
  - Rollback the changes in 2.1.0 . prefetch_count only belongs in the input plugin
* 2.1.0
  - Add prefetch_count config option
* 2.0.3
  - Add heartbeat setting
  - Add connect_timeout setting
* 2.0.0
  - Make LS2 compatible
* 1.0.1
  - Initial Release