Bump to 0.10.9

[arqunis]

This prepares for the release of 0.10.9 by updating the CHANGELOG.md file and updating the version in relevant places.

This is a release to play catch-up with Discord's new additions to its API, while expanding, improving, and fixing ours. Notable changes include:

• The switch to version 9 of Discord's Gateway and HTTP APIs.
• Support for threads.
• Support for stage instances.
• Support for sending multiple embeds in a message.
• Fixing and extending the collector API -- it is now possible to await events other than MESSAGE_CREATE or MESSAGE_REACTION_ADD.
• Clarification of slash commands in documentation (they are now fully referred to as 'application commands').
• Redesign of the Parse trait to allow parsing more model types and in application command contexts.

Huge thanks to @HarmoGlace for implementing Discord's new features.

The full, unsullied changelog for the release that will be put on Github's releases is:

---

Thanks to the following for their contributions:

• @acdenisSK
• @adumbidiot
• @Dinnerbone
• @drklee3
• @HarmoGlace
• @kangalioo
• @KangarooCoder
• @kotx
• @MelonShooter
• @rasm47
• @sbrocket
• @Splingush
• @squili
• @vicky5124

Added

• [model] Add model methods for creating public and private threads (@acdenisSK) c:dbf4d68
• [client/cache] Add support for defining cache settings in the Client builder. (@Splingush) c:ea8ec29
• [builder] Add 'number' type to ApplicationCommandOption (@Splingush) c:312ae16
• [collector] Add a generic collector for events (@sbrocket) c:3117f1d
• [model] Mention the type of event that failed to deserialise (@acdenisSK) c:1d446fe
• [model] Add methods to Event to get related user, guild, channel, and message IDs (@sbrocket) c:0aa1a6c
• [model] Derive PartialEq, Eq, PartialOrd, Ord, and Hash for UserPublicFlags (@KangarooCoder) c:e7ba5bf
• [cache] Add method Cache::channel_messages_field (@kangalioo) c:ca02662
• [http/builder/model] Add support for generation of invite links with custom OAuth2 scopes (@vicky5124) c:50cd285
• [model] Switch to API v9 and add support for threads (@HarmoGlace) c:4c53b48
• [model] Add field Guild::stage_instances (@HarmoGlace) c:13cf056
• [model] Support stage instances (@HarmoGlace) c:3e6d131
• [model] Add support for guild search members endpoint (@drklee3) c:09b523d
• [model] Add avatar field to member update event (@drklee3) c:4f488f8
• [http] Add support for fetching the current user's connections (@Dinnerbone) c:6a400f9
• [http] Allow passing bearer tokens to Http::new_with_token (@squili) c:537753b
• [model] Add support for per guild avatars (@drklee3) c:eb09d13
• [builder] Support sending multiple embeds in a message (@drklee3) c:e215c9d
• [model] Add support to (Partial)Guild::nsfw_level (@HarmoGlace) c:59ab451

Changed

• [utils] Redesign the Parse trait and add support for most applicable model types (@kangalioo) c:eb14984
• [http] Include Discord's error explanations in http::Error's Display implementation (@kangalioo) c:ce97f9e
• [model] Separate interaction stuctures per kind (@HarmoGlace) c:2b2006c
• [misc] Move workspace up to repo root, instead of under examples (@sbrocket) c:46ace1f
• [model] Clarify slash commands implementation (@HarmoGlace) c:ae09e57
• [builder] Improve implementations of embed methods on Message builders (@kangalioo) c:0be7d1a
• [model] Guarantee the Interaction::user field (@HarmoGlace) c:9d18334

Fixed

• [model] Make GuildChannel::send_message work in threads (@kangalioo) c:fb203ae
• [model] Fix broken GuildChannel collector functionality (@kotx) c:413e3ef
• [model] Handle flags in MessageUpdateEvent (@sbrocket) c:6192107
• [builder] Clear the flag when passing false to EditMessage::suppress_embeds (@sbrocket) c:47b9afb
• [builder] Fix cliend_id typo (@vicky5124) c:5cb9cb9
• [misc] Apply automatic clippy fixes (@sbrocket) c:988bfcf
• [model] Default certain select menu fields that might not be always present (@HarmoGlace) c:87564a4
• [collector] Lazily clone structs only when collector filters are actually matched (@sbrocket) c:695bbef
• [misc] Replace unnecessary guild cloning with cheaper alternatives (@MelonShooter) c:fb83066
• [misc] Fix and/or remove broken links in documentation comments (@rasm47) c:504f5a4
• [model] Skip serializating Interaction's Option fields if they are None (@sbrocket) c:c21f052
• [collector] Remove collectors that have closed receivers (@drklee3) c:d3cf53a
• [model] Update all cached guild fields on guild update (@drklee3) c:7a7e8cc
• [client/http] Fix validation error in the last step of parse_token (@adumbidiot) c:3fba372
• [builder] Fix CreateSelectMenuOption's description method (@HarmoGlace) c:cb30408
• [builder] Re-export forgotten builder types for select menus (@acdenisSK) c:5d50c56