Currently the server would set 'application/octet-stream' for all
objects, set this value based on the file extension transparently.
This is useful in case of minio browser to facilitate displaying
proper icons for the different mime data types.
- limit list buckets to limit only 100 buckets, all uppercase buckets
are now lowercase and work transparently with all calls.
- Change disk.Stat to disk.GetInfo and return back disk.Info{} struct.
- Introduce new ioutils package which implements ReadDirN(path, n),
ReadDirNamesN(path, n)
