RFC6154 (2011): `SPECIAL-USE` (mailbox attributes are in IMAP4rev2)

[nevans]

https://www.rfc-editor.org/rfc/rfc6154.html

• Add and document flags from RFC9051 #28
• RFC5258 (2008): LIST-EXTENDED (mostly included in IMAP4rev2) #43
• update documentation for #list
• update documentation for #create