• Merged the stalwart-jmap, stalwart-imap and stalwart-smtp repositories into
  stalwart-mail.
• Added support for LDAP and SQL authentication.
• Added support for subaddressing and catch-all addresses.
• Added support for S3-compatible storage.
• Removed clustering module and replaced it with a FoundationDB backend option.
• Integrated Stalwart SMTP into Stalwart JMAP.
• Rewritten JMAP protocol parser.
• Rewritten store backend.
• Rewritten IMAP server to have direct access to the message store (no more IMAP proxy).
• Replaced actix with hyper.