defcard-rg without a name causes compilation error

[green-coder]

Minimal code to reproduce:

(defn hello []
  [:div "hello"])

(defcard-rg
  [hello])

;; [Figwheel:SEVERE] java.lang.ClassCastException: clojure.lang.Cons cannot be cast to clojure.lang.Associative

I suspect that the problem is related to devcards.core/merge-options and macro expansion.

[green-coder]

I would like to propose to change the default value 'reagent-card used for the name, as it is likely that the user will use it by luck and run into unexpected behaviour - as I did.

'__reagent-card would be better.

Same remark for 'card -> '__card

[green-coder]

It appears that the compilation error is happening because of the assoc at https://github.com/bhauman/devcards/blob/master/src/devcards/core.clj#L154 which is applied onto unevaluated code from devcards.core/merge-options.