Fix response handling in authentication

[avitex]

Closes #35

• Auth responses being handled (sasl working now)
• Useless debug field removed - breaking change
• More unsolicited messages handled on auth - breaking change
• Consume mutable authenticators (to support SASL mechs better) - breaking change
• Improved client debug (buffer formatting was far too long)
• Fixed clippy warnings

[link2xt]

It works:

 WARN  repl > src/imap/mod.rs:309: Cannot login as "...yandex....". Please check if the email address and the password are correct. (no response: code: None, info: Some("[AUTHENTICATIONFAILED] AUTHENTICATE invalid credentials or IMAP is disabled sc=..."))

Also connects when IMAP is enabled.

[dignifiedquire]

thanks