Update to lua 5.4

[Kozova1]

Lua 5.4 was recently released. When will TIC-80 update?

[nesbox]

We still have 16 opened issues https://github.com/nesbox/TIC-80/milestone/25

[nesbox]

5.4 has some incompatibilities with the previous version https://www.lua.org/manual/5.4/manual.html#8

[farvardin]

there is really no need to hurry to "update" to lua 5.4

[TomatoCo]

there is really no need to hurry to "update" to lua 5.4

5.4 is notably more performant, so that's a compelling reason.

[aliceisjustplaying]

One, somewhat hackish way of solving this would be to add Lua 5.4 as a separate option and enable it via a magic comment like -- lua: 5.4 at the beginning of the cart.

And then old carts still default to 5.3.

I don't love it, but I do think this would be the best way forward.