code: function(bucket, username, password) {
      this.bucket = bucket;
      this.username = username;
      this.password = password;
  
      this.authString = ["Basic", base64.encode([username, password].join(":"))].join(" ");
      this.baseUri = BASE_URI + bucket;
  
      this.baseHeader = {
          authorization   : this.authString,
          host            : "v0.api.upyun.com"
      };
  }
docs: Upyun class
  @param bucket
  @param username
  @param password
  @constructor