v0.7.0 - Release train continues

• Overhaul voice support for 1-on-1 and group calls
• Add LiveServer::permissions_for to calculate member permissions
• Allow disabling voice support using Cargo features
• Move member sync methods to Connection rather than State
• Cleanly disconnect in Connection::shutdown
• Store discriminators as u16 rather than String
• Implement Display for ID types, printing just the number
• Change Error::Closed to contain a decoded String
• Discord changes
  • Reaction support
  • Remove xkcdpass from invites
  • Add message pinning events
  • Add permissions: administrator, external emojis, add reaction, manage webhooks
  • Implement guild sharding and gateway v6
  • Implement Discord's official rate limit handling
  • Compression support in READY and GUILD_CREATE
  • Message delete bulk event
  • More fields in UserSettings
• Rest API additions
  • create_permission, delete_permission
  • get_application_info
  • get_server_channels
  • get_unresolved_incidents
  • suggested_shard_count
• Update version of various dependencies