add rockspec and structure folders

This gets you set up to submit this as a luarock. Luarocks are Lua's common module system (like Ruby's gems, or Node's npm.)

Once this is done, you can:

> send the rockspec to the LuaRocks mailing list and we'll include it in the public LuaRocks repository. We will usually publish both the .rockspec file and the appropriate .rock file in the server.
>
> http://luarocks.org/en/Creating_a_rock

You could also, if you'd like, submit it to an alternate server at http://rocks.moonscript.org.

This also assumes a license of "MIT". Since you don't have a license listed, that may need to be adjusted. Let me know if I can make any changes or explain anything I've done!