Sean T Allen

@stefandd I'm going to set this as a draft PR.

@stefandd please let us know when this is ready for review.

@kulibali I've updated this to try benchmark 1.7.1

I'll squash and merge this tomorrow.

@ergl Type aliases dont appear in any generated documentation.

I rebased this against master.

@jemc do you know why we never merged this? Also, there are two failing tests now, would they be expected and need to be updated for this change? ``` [...

If this was going to be merged, it needs release notes.

I think the most reasonable thing for this given that ```pony class Foo new create(a: U32) ? => if a > 10 then error end actor Main new create(env: Env)...

I prefer the code as is. There final product should be identical but the existing is less error prone in my mind.