troposphere 3.0 - futures

Wanted to start an issue to discuss goals for troposphere 3.0:

- [All core code gets generated from the resource specs](https://github.com/cloudtools/troposphere/issues/618)
- [Python 3+](https://github.com/cloudtools/troposphere/issues/1295) (remove the EOL python2 support)
- [Restructure in a way to allow intellisense to work with properties to make coding easier](https://github.com/cloudtools/troposphere/issues/1462)
- Maintain core backward compatibility

Implications:
- Validators and other non-generated code will be merged in (likely from separate files using object mixins)
- Align/rename with the AWS resource spec naming where possible
- Likely will have some breaking changes due to name changes (hence a major release)