NAN 1.5 WIP

This branch will become NAN 1.5.
Added Asyncworker #207 and new NanNew #210. Needs more testing with actual addons.
Now split into many files. Seems to work so far. Good news for nauv.h
Why do you use `class` instead of `struct` here? It triggers a warning on my end:

````
../../nan_new.h:65:1: warning: 'Factory' defined as a class template here but previously declared as a struct template
      [-Wmismatched-tags]
class Factory<v8::FunctionTemplate> : public FactoryBase<v8::FunctionTemplate> {
^
../../nan_new.h:36:23: note: did you mean class here?
template <typename T> struct Factory;
                      ^~~~~~
                      class
````