S5cmd

- Fix get/cp without 2nd param or exact destination filename.

- Implement shell auto completion.
- Add context support for batch AWS requests.
- Implement "s5cmd get".
- Reduce idle-timer values.
- Add option -vv to log parser errors verbosely.
- Implement "du -g" to group by storage class.

- Use Go bool type instead of aws.Bool on recoverer.

- Make RequestError retryable.

- Implement verbose output (-vv flag).
- Add godoc for error types.