v0.6.0 - More functionality, Discord changes

• Natively support auto-reconnection and resuming the previous session
• Add utility methods to generate mentions for users, roles, and channels
• Fix errors relating to missing read_state
• Fix current voice channel going out of sync when forcibly moved
• Replace Event::Closed with Error::Closed, with more information and better structure
• Model support for:
  • Unavailable servers
  • Nicknames
  • Role mentionability
  • "Now streaming" presences
  • Pinned messages
  • User notes
  • 2FA information
  • Existing fields now present on Server
• Expand capabilities of edit_server: owner, verification level, and splash
• New REST wrappers:
  • Server prune
  • Get active and upcoming maintenances
  • Get server member
  • Pin and unpin messages
  • Get messages around a specific message
  • Delete messages in bulk
  • Edit user notes

Thanks to @taiyaeix and @nstafie for their contributions to this release.