Lua 5.4 breaking changes revision

[bananu7]

I've noticed that 5.4 is breaking a lot of compatibility with 5.1 and 5.2 that 5.3 preserved. Because of that, I'll need to decide whether Turnip goes all in on the new version, or keeps to support the older ones.

Here's a handy list stolen from the Ravi language readme:

Feature.	Ravi	Turnip
Generational GC	Yes	Maybe
New random number generator	Yes	Maybe
Multiple user values can be associated with userdata	under consideration.	Probably
const variables	not planned	#74
close variables	'defer', no plans to support	Maybe
Interpreter performance improvements	No	No (it relies to C impls)
Table implementation changes	under consideration	No idea
String to number coercion is now part of string library metamethods	Yes	Probably
utf8 library accepts codepoints up to 2^31	Yes	Definitely
Removal of compatibility layers for 5.1, and 5.2	No, Ravi supports 5.1&5.2	Maybe