update to working with elixir 1.0.0

- record transformed to struct
- update to new ast case clauses generation
- use for instead of lc
Do you need this on 0.15? I kind of don't like this requirement because it allows too many versions (e.g. 2.0 once it comes out). If it's ok with you, I'd rather have `"~> 1.0"` here.