Lua: don't create globals

[hryx]

When calling require('libmodipulatelua') it creates a global table called "modipulate" containing the needed functions. This practice is frowned upon by some -- the nicer way to do this is have it return the package. Then you can use it like this:

local modipulate = require('libmodipulatelua')
modipulate.init()
modipulate.loadSong('poop.xm')

Disclosure: I haven't made any C modules for Lua, so I don't know if there any gotchas in making it behave this way.