support for logging Clojure data structures

We could specify a structured format and a wire protocol for printing/expanding Clojure data structures in a similar way how cljs-devtools work for ClojureScript.

cljs-devtools could then connect to a backend library via websocket and act as a rich logging console for Clojure projects. With support from [Dirac DevTools](https://github.com/binaryage/dirac) we could turn Chrome's DevTools into a nice REPL + logger for Clojure (not only for ClojureScript).

I personally do most of my work on client-side, so it is unlikely for me to spend time on it at this point. But I would be happy to help someone else who would be interested in implementing it to integrate it (I would do the JavaScript part on front-end).

The issue names no files, tests, or entry points. Start by reviewing cljs-devtools and Dirac DevTools, then define the structured format and websocket protocol needed to print and expand Clojure data structures; done means a backend can connect to a rich Chrome DevTools logging console.

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