Change `parse_message_delete_bulk` to not dispatch individual
`message_delete` events, and instead `bulk_message_delete`. Also make
`raw_bulk_message` delete and `raw_message_delete` have message
objects attached.
Fixes#1807
This allows for internal changes in Discord to not cause a breaking
change every time something changes.
Also implements #1214 which adds guild_id to every event where
applicable.
This is a breaking change.