code: func NewMailjetClient(apiKeyPublic, apiKeyPrivate string, baseURL ...string) *Client {
  	httpClient := NewHTTPClient(apiKeyPublic, apiKeyPrivate)
  	smtpClient := NewSMTPClient(apiKeyPublic, apiKeyPrivate)
  
  	client := &Client{
  		httpClient: httpClient,
  		smtpClient: smtpClient,
  		apiBase:    apiBase,
  	}
  
  	if len(baseURL) > 0 {
  		client.apiBase = baseURL[0]
  	}
  	return client
  }
docs: // NewMailjetClient returns a new MailjetClient using an public apikey
  // and an secret apikey to be used when authenticating to API.