Add FastSignal as an alternative/replacement to GoodSignal

[lucasmz-dev]

FastSignal when referred here is not the alternative provided to GoodSignal by their own post. This is a library I made; It isn't actually as speed focused as GoodSignal, despite the name, I've been thinking of changing it to BetterSignal but that just sounds problematic... Anyhow..

This implements a proposed solution at solving #463.

This pull request has as its objective:

• Add FastSignal
• Default to it

This could actually replace both, the Signal.lua implementation, and GoodSignal, but at this time I'm only adding it as an alternative, I am open to changing this on how it is decided to implement this.

Need review:

• If my code is correct, I do not necessarily use NevermoreEngine itself, and I'm not sure if my modifications make sure inside the engine, please review.

Fixes #463

[lucasmz-dev]

I am not really able to test things here out, I am not really in Roblox development and can't be anymore properly due to Roblox's decision to not support Linux :(, just noticed this issue and wanted to note to it. Therefore, the changes made here are minor so that there aren't any issues I can't debug and such.