Add rockspec

[leso-kn]

Hi :) This PR adds a package definition for LuaRocks and adds compatibility for Python 3.11+.

I took the liberty to prepare a demo rock under https://luarocks.org/modules/leso-kn/lunatic-python, so you can try out the PR from my unmerged feature branch using:

> luarocks install lunatic-python

Python can then be used from inside Lua, e.g.:

-- test.lua
local py = require 'python'
py.execute 'print("Hello from Python inside Lua!")'

In case you prefer to not include this or when it gets merged, I'll of course delete my version on luarocks.org so you can upload under the package name 'lunatic-python'.

Thanks for keeping this project up!

[leso-kn]

Small edit: I've corrected the license field in the rockspec to LGPL-2.1, had put MIT out of habit accidentally.