v2.1.0

• The MailClient.deleteMessages() / undoDeleteMessages() as well as the moveMessages() and undoMoveMessages() calls
  will now update the given messages UIDs automatically, when they have been specified.
• Simplify building a multipart/alternative message or message part by adding the option plainText and htmlText parameters
  in MessageBuilder.prepareMultipartAlternativeMessage() and addMultipartAlternative().
• Fixed documentation for generating a mime message with an attachment (thanks lqmminh!).