#100 - Chat history

[mixxorz]

Issue ticket #100

If applied, this PR will...

Add support for Prat's History module.

Please provide detail on the technical changes, if relevant

Add BackFillMessage method on SlidingMessageFrame to prepend a message to the beginning of the stack.

Screenshots

Dev checklist

• [x] Feature works with other addons enabled
• [x] Feature works with all other addons disabled
• [x] README updated (if necessary)
• [x] CHANGELOG updated