Implement RESTful API using url pattern and http method

[ardeness]

• url should be
  /
  /{bucket_id}/
  /{bucket_id}/{object_id}

• CRUD matches with http method
  eg)
  "GET /" : listing bucket
  "GET /{bucket_id}" : listring objects in bucket
  "POST /{bucket_id}" : Upload and create object in bucket
  "GET /{bucket_id}/{object_id}" : GET object
  "DEL /{bucket_id}/{object_id}" : Delete object

• Return proper http status code
  eg)
  "GET /{bucket_id}" : 200 on found, 404 when bucket is not exist, and so on