Allow packing of arrays with {pack_str, from_list}

[cleverfox]

Hello. Today for I have a little patch for your review. In my project I use binaries and strings simultaneously and had no problems before today. Now I also needed to use arrays (with strings and binaries) and got few problems. I guess special tag for arrays will be useful in case if default behaviour should be strings and you need arrays very seldom. Lists tagged with {array, List} will be forcely encoded as arrays.