Cachedir fix

> I think i fixed Issue #3 by using os.tmpname() to get a temp file instead of using vlc's cache dir.

os.tmpname() just return a random string (at least on windows if I remember correctly). I don't consider using C: as a good option, it's not safe and not clean (leave garbage file if an error occur for example).
I think it would be better to use with os.execute("mkdir " .. vlc.config.cachedir()) instead.