[Review][returned for revision] SE 0192 - Non-Exhaustive Enums

The review of "SE 0192 - Non-Exhaustive Enums” had extensive discussion and has been returned for revision.

The proposal author, Jordan Rose, is working on a revised proposal that includes:

- Alterations to the naming of the attributes.
- New affordances for how switch statements work with non-exhaustive enums.

There will be a second round of review, but there is active discussion considering the latter point right now on swift-evolution on the thread "Handling unknown cases in enums”:

  https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20180108/042604.html

I encourage anyway interested in that topic to follow/participate in that thread.

Ted