snappy version 3 - work in progress

Complete simplified rewrite of snappy.
Hey, thanks a lot for the feedback! That sounds completelly reasonable, taking the underlying `char *` would be the right way to do it (since the input could be a `String`)

I've added you as a contributor to this repo, so if you'd like to add that yourself that would be highly appreciated. Otherwise I'll take a look at it myself a little later.