code: function encodeAttachmentMSTTransfer(buffer, offset, symbol, quantity) {
      if (symbol == undefined)
          throw Error('Specify output asset');
      if (quantity == undefined)
          throw Error('Specify output quanity');
      offset = buffer.writeUInt32LE(Constants.MST.STATUS.TRANSFER, offset);
      offset += encodeString(buffer, symbol, offset);
      offset = bufferutils.writeUInt64LE(buffer, quantity, offset);
      return offset;
  }
docs: Helper function to encode the attachment for an asset transfer.
  @param {Buffer} buffer
  @param {Number} offset
  @param {String} symbol
  @param {Number} quantity
  @returns {Number} New offset
  @throws {Error}