Support special characters in folder names

[LinqLover]

In my HPI mailbox, I have a folder named foo\bar (the backslash matters). When downloading all mails, the IMAP client is unable to parse this folder because the server answers a multiline response for this folder. This means that in ICEndPoint >> #fetchNextResponse, the relevant folder description will be spread over multiple evaluations of self stream lastResponse. This requires a minor design change to detect the special escape syntax for these responses. Please contact me if you need further information.