Implement ImapFolderAgent.
Define expected payloads and reuse them.
Include "folder" in events.
Cover the "mark_as_read" option.
Check regexp validation.
Convert 'port' to integer.
Unbreak with Ruby <2.0 not having File::FNM_EXTGLOB.
Elaborate on how to specify a case-insensitive pattern.
Mark duplicated mails as read even if event creation is skipped.
Document how this type of agent memorizes and deals with already seen mails.
Merge pull request #328 from knu/imap_folder_agent

Implement ImapFolderAgent.