Add callback handler to NodeJS binding similar to Go bindings

[venediktov]

Currently NodeJS bindings only allow to start vanilla-rtb bidder as a library , but it does not provide
a callback handler to intercept events from vanilla-rtb bidder nor it provides access to our
partitioned cache aka matchers used by bidder.
Would it be needed to have something that allows developers to intercept events from bidder and process them in NodeJS ?
Does anyone need to access our partitioned cache structures from within JavaScript ?

• at least add callback handler to nodejs/bidder_binding.cpp