Duktape

* [ ] Waiting for duktape core regexp improvements to support CoffeeScript https://github.com/svaarala/duktape/issues/86
* [ ] Investigate duktape.rb CommonJS support. Does it even work? Can it be neutered with first class apis?
* [ ] Improve duktape.rb exception subclasses. Pretty much everything is a "context error".
* [ ] Improve "complex" object return values. Anything thats JSON serializable should be okay to return. Forced to JSON stringify and return all objects out as strings of JSON.
* [ ] `eval` must be written in terms of `exec` instead of the other ways around. Improved return values could fix this.
* [ ] `call_prop` can't be used directly because of reasons above. Must resort to eval.

/cc @judofyr @sstephenson @dgraham