Param names in ast v2

[fran-worley]

This updates the AST to include predicate argument names and is a much cleaner solution than #13.

@solnic your thoughts please?

[fran-worley]

We've got to add specs to the rule compiler & update it to work with the new ast https://github.com/dry-rb/dry-logic/blob/master/lib/dry/logic/rule_compiler.rb#L54

[solnic]

We made it 🎉