0.2.0

• Added a Mailgun transport (US and EU regions), sending the assembled message as MIME.
• Added a Resend transport.
• Bcc recipients on API sends are now carried as an explicit envelope and the Bcc header is stripped from the delivered message, so hidden recipients are never disclosed to other recipients.
• Any setting can now be pinned in wp-config.php as an upper-case constant; a pinned setting renders read-only on the settings page and is left untouched when the form is saved.
• Added an admin notice when a send fails, so a silently broken mailer is noticed. It clears itself after the next successful send.
• Added WP-CLI commands: wp lean-smtp test [<recipient>] and wp lean-smtp status.
• The API transports now share one message assembly behind a Lean_SMTP_Api_Transport interface, so all of them reproduce core's wp_mail() semantics identically.