• #347: Add hooks that run for the "extract" action: "before_extract" and "after_extract".
• #350: Fix traceback when a configuration directory is non-readable due to directory permissions.
• Add documentation navigation links on left side of all documentation pages.
• Clarify documentation on configuration overrides, specifically the portion about list syntax:
  http://torsion.org/borgmatic/docs/how-to/make-per-application-backups/#configuration-overrides
• Clarify documentation overview of monitoring options:
  http://torsion.org/borgmatic/docs/how-to/monitor-your-backups/