Migrate to use callback's with async_resource instead of deprecated callbacks.

[jostrander]

  CXX(target) Release/obj.target/mouse-forward-back/mouse-forward-back.o
../mouse-forward-back.cc: In function ‘void MouseForwardBack::events_callback(uv_async_t*)’:
../mouse-forward-back.cc:55:24: warning: ‘v8::Local<v8::Value> Nan::Callback::Call(int, v8::Local<v8::Value>*) const’ is deprecated [-Wdeprecated-declarations]
         cb.Call(1, &arg);
                        ^
In file included from ../mouse-forward-back.cc:1:0:
../node_modules/nan/nan.h:1740:3: note: declared here
   Call(int argc, v8::Local<v8::Value> argv[]) const {
   ^~~~
  SOLINK_MODULE(target) Release/obj.target/mouse-forward-back.node
  COPY Release/mouse-forward-back.node