[WIP] NOTIFY Command

[jkaessens]

Once finished, this implements the IMAP NOTIFY extensions as discussed in issue #63. Currently work in progress.

Todo:

• handle untagged STATUS responses in mailbox parser (done in 5d19d4f)
• handle NOTIFY SET STATUS where STATUSes are sent right after the NOTIFY command (done in f6b6c96)
• handle asynchronous STATUSes (done in 6e48c77)
• implement @jonhoo's suggestions about better style (done in 855abc5)
• make all results ZeroCopyResult

[coveralls]

Coverage decreased (-4.8%) to 84.726% when pulling 855abc5 on jkaessens:notify into dc21eae on mattnenterprise:master.

[jkaessens]

@jonhoo Hey, it would be nice if you could take another look at the code. I implemented all that has been missing (for now) and also your suggestions. Test runs fine and an actual test against an actual IMAP server with quite a few mailboxes also works.

[jonhoo]

Hey, sorry, I completely dropped the ball on this one! Can you match up with master (which now also has the structured responses stuff merged) and I'll review? I noticed you'd also like to add ZeroCopyResult, but are there any other changes you expect to make to this?

[jkaessens]

Hey, no problem. I've been busy with offline stuff anyway. I just matched up with master but I haven't looked into the structured responses and ZeroCopyResult, yet. Maybe I find the time in the next few days.

[jonhoo]

It'd be nice if you could rebase this onto master instead -- makes the commits a little nicer to follow. I don't think it should be too painful given that master hasn't changed substantially :)

[jonhoo]

@jkaessens I've had to move the repository under my own control so that I can set up CI and such correctly following the resolution to #69. Could you please open this PR up again against https://github.com/jonhoo/rust-imap instead? Including a link back to this for reference would probably also be a good idea!