Fix IMMUTANT-328, and a doc tweak

This worksforme.  If you'd like to test with some accessible, widely-used middleware, [Piggieback](https://github.com/cemerick/piggieback) is a reasonable option, as are the various ritz bits.

Let me know if there's anything that should be done differently given the operational context.  I'm a bit nervous about the `eval` in there, but that's the nature of what `:nrepl-middleware` accepts ([see sample usage](https://github.com/technomancy/leiningen/blob/stable/sample.project.clj#L151), and [real-world usage](https://github.com/cemerick/data.generators/blob/master/project.clj#L42)).  Happy to revise as needed, etc.