*print-fn* / dynamic vars

[borkdude]

*print-fn* controls printing in CLJS. with-out-str build on that (#31). This brings up the question if we should have dynamic vars that you can set! and use with binding or if we want to deviate from CLJS here. *print-fn* could also just be an atom.

[borkdude]

I thought a little bit more about the mutable es6 exports.
I think we could maybe just do this as well:

(def x 1)
=>
var x = 1
function _set_x(v) {
x = v;
}
export {x, _set_x}
and then we can always leverage _set_x to make mutations

[borkdude]

Thought about it some more: this won't work with changing the module over time, it will only work for things that were already defined in the module, but you can't add extra stuff to the module.
So the .dev.js output should maybe just use global nested objects as modules (can always mutate and add stuff) and the .js (production output) should just be the finalized es6 output