Purge messages by time interval

[erkinalp]

#208 (comment)

We'll be introducing a proper "purge channel" endpoint at some point in the future - which will be able to delete old messages without creating excessive table fragmentation (we already have a plan on how to do so).

The endpoint design could be quite simple (POST /channels/:id/purge in my proposed design). It should have two parameters:

before: the largest message snowflake, inclusive (if omitted, from the time of invocation)
after: the smallest message snowflake, inclusive (if omitted, from the channel create)

and yes, defaulting to wholesale blanking of the channel is intentional

Guild members with MANAGE_MESSAGES AND MANAGE_CHANNELS in the respective channel and guild owners should be able to invoke this operation. No limits on the number of covered messages should be imposed.
I've done a test implementation of it in my own reimplementation of Discord API, turns out the code required is actually just about 50 lines if you don't consider table fragmentation in any way whatsoever.

Clients should still receive MESSAGE_BULK_DELETE events (yes, events, one for every 100-ish messages) with all affected message IDs, to be able to know which messages they should drop without having to do an expensive lookup.