Merge in_tail_ex features into in_tail. refs #269

Last step of #269 , merge in_tail_ex into in_tail.
The different from original in_tail_ex is below:

- `refresh_interval` is `nil` by default. The user should set `refresh_interval` for watching new files
- expand_date is always `true`

This pull request changes in_tail internal, so I need some testers.