Importer: General overhauling

* Fixes the async crashing by explicitly
  closing async.
* Changes the behavior of renderSync importer
* Updates index accordingly.
* Removes obsolete tests accordingly.

BIG THANKS to @txdv and this addresses #586 ! :tada::+1:

**Need to update the docs accordingly.**

---


Code: Adds NanScope() to guard nan handlers.
* Fixes for Persistent.
* Credit @kkoopa (thanks @kkoopa for pointing these out!).
 
`function done(data)`