Implemented Nan and aligned to segfault_handler naming convention

This is a breaking change as it names the module segfault_handler with an underscore to make the build and sample code work. 
On the upside it implements Nan change and so should run on later version of node. 
Would recommend publishing in npm as segfault_handler too for consistency and maybe removing/deprecating the current 2.1 in there. 

Yes this is a breaking change and I mentioned in the initial pull comment that you might want to republish as ```segfault_handler``` on npm and depricate this?