Preload other lua files

[whati001]

Hi Gopher-lua team,

seems like there is no convenient function to preload entire LUA files into the current State.
There is a ISSUE-119 showing a workaround, but I would really love to see this feature provided by the LState instance inself
For example a look like this wold do the job:

func (ls *LState) PreloadFile(path, name string) error {
	fmod, err := ls.LoadFile(path)
	if err != nil {
		return err
	}
	preload := ls.GetField(ls.GetField(ls.Get(EnvironIndex), "package"), "preload")
	if _, ok := preload.(*LTable); !ok {
		ls.RaiseError("package.preload must be a table")
	}
	ls.SetField(preload, name, fmod)
	return nil
}

By leveraging the code above, we could outsource common logic into LUA "utility" files and load them by multiple other ones.
For example:

1) outsource complex computations:
utils.lua

local utils = {}

function utils.addtwo(a, b)
    return a + b
end
return utils

2) preload them within the main.go

func main() {
       // ...
	// preload some other local lua file
	if err := L.PreloadFile("./lua_scripts/utils.lua", "utils"); err != nil {
		panic(err)
	}
       // ...
}

3) Use the functions in other lua files
mainlogic.lua

local utils = require("utils")
print(utils.addtwo(4,5))

What do you think about this feature request?