[Le #151] Replace instances of manual de-structuring of error maps with (ex-triage)

[stanislowskij]

⚠️ Imported from legacy repository. This issue is a duplicate of Clojure-Intro-Course/babel-legacy#151.

A handful of functions in processor.clj use giant let blocks with heavy de-structuring to parse relevant portions of error data, as returned by functions like (Throwable->map).

Consider using clojure.main/ex-triage instead to simplify the data we are passing around and make extracting values easier, as it seems to do a lot of the heavy error analysis for us.