Provide a new alias for Any, dedicated for use as a placeholder, thus reserving Any for situations when truly every type is acceptable.

When adding type annotations to code that was previously untyped, it's often useful to do so in stages. A common early step is to use Any liberally to avoid getting stuck figuring out the "best" type for a Var. (For example, see this pull request, in which clojure.zip/zipper is given the type [Any Any Any Any -> (Vec Any)].)

The problem is that there's no way to tell whether a given occurrence of Any is functioning as a temporary placeholder, or whether it's expressing the fact that truly every value is acceptable.

I propose a new alias for Any that will enable users to distinguish between these two usages. I don't feel strongly about the name of the alias, but in the absence of other suggestions I nominate Dunno because it concisely expresses the phrase "I don't know".