Exposing a distinct "value" parameter for enumeration members, to avoid relying on default toString()

[blast-hardcheese]

• def value: String on containing enumeration could be a val value: String if you prefer. I think having a weak reference there is better for some reason, but I can't remember why or if this is true.
• This is motivated by having been bit by refactors that change a member from a discrete type to an Option[A] or List[A] or otherwise, but relying on the default .toString() doesn't flag this as an error. This also provides an alternative for those using wartremover's ToString wart, which prevents relying on the default toString as well.

This was able to be merged without conflict after applying #934, another reason for not changing too much about emitted classes

[ghostdogpr]

LGTM!