Using allSatisfy with template that takes multiple type arguments

[Andrej Mitrovic]

Actually now that I think about it, isOneOf!() is more to my liking.
isImplicitlyConvertible allows too much, e.g. implicit casting of
unsigned to signed. Even though that might be perfectly valid, I want
to optionally allow a warning via a version switch. So I'll be using
isOneOf.