[Dr. McKay]

This plugin should, in theory, stop the original Machina double kill sound and play a custom sound located at sound/machina_doublekill_custom.mp3, but it's my first time writing a plugin like this, so don't blame me if it doesn't work.

I might properly release it later once I test it and refine it. I'm sure the volume of the original sound can be overridden without needing a custom file, but this offers more flexibility, for custom sounds and such.