Support lua 5.5

Hi Albert 👋 

We're currently doing rebuilds for Lua 5.5 on Arch Linux.

I noticed that your project is only compatible with Lua 5.4 and that i need to patch the Makefile (no biggie).
Either way, it would be great if pd-lua could support Lua 5.5 in the future and this ticket is basically here to track any progress on it! :)

Greetings!