Add comments (DocBlock)

Hi,

As promise, the "Docblock" part of pull-request #12 
My English is very basic, if you have remark about the documentation, it would be great !

Thanks for your work.
Best Regards
@fezfez I agree with @umpirsky, don't fight against the language. We know it's null already.
This variable will become null at *instantiation* and not before, so putting this in the class (blueprint) declaration is worthless imho.