func GetRequestSubuser(key, endpoint, host, subuser string) rest.Request {
	return createSendGridRequest(sendGridOptions{key, endpoint, host, subuser})
}
GetRequestSubuser like GetRequest but with On-Behalf of Subuser
@return [Request] a default request object
package sendgrid
import (
	"github.com/sendgrid/rest"
)
type sendGridOptions struct {
	Key      string
	Endpoint string
	Host     string
	Subuser  string
}
func GetRequest(key, endpoint, host string) rest.Request {
	return createSendGridRequest(sendGridOptions{key, endpoint, host, ""})
}