prefer defining react var instead of assuming it on global namespace

[carocad]

Hey @dmotz,
I saw that in the code you use js/ReactNative to get the current instance of ReactNative. However that way the user is forced to put ReactNative in the global scope, which shoudnt be a requirement IMHO. That is specially problematic if a user require the macros of this library before setting that up.

I think there are some libraries that define the js/ReactNative as global but I dont think is the case for all cljs libs out there. I would propose something like reagent approach. Basically if the object is already defined globally then rely on that, otherwise require it.

Let me know your thoughts :)

[dmotz]

Makes sense, will address in the next update.

[carocad]

thanks 👍