Handle multi fetch failure gracefully

When a fetch fails (often because a locally backed-up folder no longer exists on the server), simply log an error an continue.

Update flags in transactions and deprecate Ruby 2.x

Changed

• Implemented update in transactions. Previous only appends were handled.
  This allows actions which modify existing emails to be handled inside
  transactions when using the 'delayed_metadata' strategy.

• Update flags in a transaction, speeding up flag refreshes by avoiding
  repeated writes of the JSON metadata file. This is a change inspired by
  this pull request: #200.

• Deprecated Ruby 2.x Support

Handle `--mirror` in single backup

Fixed a bug in single backup where the --mirror parameter was ignored.

Added handling of `--delimiter` and `--prefix` options for `imap-backup restore`

When the server has a delimiter that is different from the default /, the user can now specify the value.

When the server uses a namespace (that was not present at the moment of backup), it is now possible to specify it.

Suppress Spurious 'Invalid File' Warnings

Suppressed mailbox and metadata '...is invalid' messages when these
files are missing. Now, the messages are printed when a file is
actually malformed.

Bugfix: corrected the behaviour of the legacy metadata convertor

Previously, mailboxes and metadata files would get deleted after migration.

Permit use of TLSv1.3

v14.5.0

Version 14.5.0

Documentation-only Release

This release serves only to update the documentation at rubydoc.info

Bugfix for container

Bugfix: check for the presence of the spec directory before conditionally activating code coverage

Split user and developer documentation

Documentation is now split into two areas:

• End-user facing: via the README on GitHub
• Developer: via a different main YARD page on rubydoc.info