func (c *Client) EnableFeatures(feature Feature) {
	c.featuresMutex.Lock()
	defer c.featuresMutex.Unlock()
	c.features[feature] = true
}
EnableFeatures enables a feature.
package messagebird
import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"net/url"
	"runtime"
	"strings"
	"sync"
	"time"
)
const (
	ClientVersion = "7.0.0"
	Endpoint = "https://rest.messagebird.com"
	httpClientTimeout = 15 * time.Second
	voiceHost = "voice.messagebird.com"
)
var (
	ErrUnexpectedResponse = errors.New("The MessageBird API is currently unavailable")
)
type Feature int
const (
	FeatureConversationsAPIWhatsAppSandbox Feature = iota
)
type Client struct {
	AccessKey     string            
	HTTPClient    *http.Client      
	DebugLog      *log.Logger       
	features      map[Feature]bool  
	featuresMutex sync.RWMutex      
}
type contentType string
const (
	contentTypeEmpty          contentType = ""
	contentTypeJSON           contentType = "application/json"
	contentTypeFormURLEncoded contentType = "application/x-www-form-urlencoded"
)
type errorReader func([]byte) error
var voiceErrorReader errorReader
func New(accessKey string) *Client {
	return &Client{
		AccessKey: accessKey,
		HTTPClient: &http.Client{
			Timeout: httpClientTimeout,
		},
		features: make(map[Feature]bool),
	}
}
func SetVoiceErrorReader(r errorReader) {
	voiceErrorReader = r
}