There is an arbitrary mapping being done right now between
nixpkgs lua infrastructre and luarocks config schema.
This is confusing if you use lua so let's make it possible to use the
lua names in the nixpkgs, thanks to the lib.generators.toLua convertor.
The only nixpkgs thing to remember should be to put the config into `luarocksConfig`
`buildLuarocksPackage.extraVariables` should become `buildLuarocksPackage.luarocksConfig.variables`
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