implements #180

1. Added phantom type parameter A to HtmlAttr, AriaAttr, and Prop to identify each attribute at the type level
2. Added ValidAttr[A, E] and ValidProp[A, E] marker typeclasses (which are not variant in E) that gate which attributes can be used on which elements at compile time
3. Add ElementScopes mapping attributes to their valid element types.
4. Updated code generators to emit phantom-typed traits and ValidAttr/ValidProp given instances
5. Preserve source compatibility for aliases like typ and tpe still work
6. changed tlBaseVersion from 0.2 to 0.3
   used the context of issue 179 and 96