func (s *CatAllocationService) Columns(columns ...string) *CatAllocationService {
	s.columns = columns
	return s
}
Columns to return in the response.
To get a list of all possible columns to return, run the following command
in your terminal:

Example:
curl 'http://localhost:9200/_cat/aliases?help'

You can use Columns("*") to return all possible columns. That might take
a little longer than the default set of columns.
package elastic
import (
	"context"
	"fmt"
	"net/url"
	"strings"
	"github.com/olivere/elastic/uritemplates"
)
type CatAllocationService struct {
	client        *Client
	pretty        bool
	bytes         string  
	local         *bool
	masterTimeout string
	nodes         []string
	columns       []string
	sort          []string  
}
func NewCatAllocationService(client *Client) *CatAllocationService {
	return &CatAllocationService{
		client: client,
	}
}
func (s *CatAllocationService) NodeID(nodes ...string) *CatAllocationService {
	s.nodes = nodes
	return s
}
func (s *CatAllocationService) Bytes(bytes string) *CatAllocationService {
	s.bytes = bytes
	return s
}
func (s *CatAllocationService) Local(local bool) *CatAllocationService {
	s.local = &local
	return s
}
func (s *CatAllocationService) MasterTimeout(masterTimeout string) *CatAllocationService {
	s.masterTimeout = masterTimeout
	return s
}