RFC: Change type of Env.root to AmbientAuth

[Theodus]

Env.root currently has type (AmbientAuth | None) to allow for creation of artificial Env instances without AmbientAuth. Yet, there is no observable usage of this feature. As it is requires extra work to make use of, as one always needs a pattern match or an as expression with a surrounding try, this RFC wants to change its type to AmbientAuth and make AmbientAuth required when constructing an artificial Env instance, until a better solution is found.

https://github.com/ponylang/rfcs/blob/master/text/0065-env-root-not-optional.md

[dckc]

Yay! I have been hoping for this change since May 2016. #301 (comment)

Env and AmbientAuth are about static properties of the code; allowing the possibility that Env ever doesn't have AmbientAuth only results in useless checks to satisfy the type checker. AmbientAuth means "whatever ambient authority main() was called with". Attempts to use that authority may fail at runtime, of course. But to put into the type the possibility that there may be no such datum introduces only cost and no gain.