Gracefully handle symbols in .cljs.edn files

[arichiardi]

At the moment, an exception is thrown when I use:

{:require [rest-resource-viz.core]
 :on-jsload 'rest-resource-viz.core/on-jsload} ;; with apex

Instead of the correct:

{:require [rest-resource-viz.core]
 :on-jsload rest-resource-viz.core/on-jsload}

It would be great to walk the edn file and warn instead. I know this opens the door to a bigger problem, that is how to validate .cljs.edn files but ... well... at some point maybe we need it.

Thanks for moving it to the new org @Deraen!

[Deraen]

Done in fbf5297

Boot-reload should do the same for :on-jsload option: adzerk-oss/boot-reload#116