rum.core/derived-atom without docs

[madstap]

rum.derived-atom/derived-atom has a nice docstring, but it doesn't transfer over to rum.core/derived-atom, which appears to be undocumented. A fix could be to move the docstring to the def in rum.core.

[tonsky]

Please provide a PR :)

[madstap]

When I'm already messing around with this particular fns metadata, would you accept that I add indentation metadata as well, so that emacs (and eventually, hopefully, other editors) indent it like:

  (def *x (derived-atom [*a *b] ::key
            (fn [a b]
              (str a \":\" b))))

instead of the current

(def *x (derived-atom [*a *b] ::key
                      (fn [a b]
                        (str a \":\" b))))

[tonsky]

sure

[madstap]

PR provided :)

[tonsky]

Thanks! Closed in #85