Example Lua extension with a single function

This is the simple branch in which all files are self contained. Other branches:

• pkg: only contains Zig package with Lua API wrapper in a Zig module
• use-pkg: contains this extension and uses the above as a dependency

Usage:

$ zig build
$ lua
Lua 5.4.4  Copyright (C) 1994-2022 Lua.org, PUC-Rio
> package.cpath = "zig-out/lib/lib?.dylib;zig-out/lib/lib?.so;zig-out/lib/?.dll"
> corncob = require("corncob")
> corncob.chomp(44)
440.0