Port to Lua 5.3

[qwertychouskie]

Probably we can use add_definitions("-DLUA_COMPAT_5_1"), but it needs to be tested.

[v1993]

It will simple make a lot of trouble, especially on Lua side.

Lua 5.1 is still used in production-ready applications and there's no real reason to get rid of it.

add_definitions is part of old CMake and should not be used anymore. To get -DLUA_COMPAT_5_1 working you must build Lua together with project, and, as I said, it will still very very likely produce troubles which aren't needed.

As a Lua guy I also have to say that cubosphere is built mostly in Lua 5.1 spirit (but it still performs pretty bad with recommended Lua ways in fact).