[dev] Extension of commentCallback

[duck]

Jan Schneider wrote:
> I understand how this may perform better. But we are talking about a  
> comment API here, and that means that all comment handling has to be  
> encapsulated. What you want to do is a hack. If you want a better  
> performing API, implemented a method in Agora that allows to retrieve  
> the number of comments in a batch mode.
I still think that we must allow this mini hack here in favor to 
usability. The problem is that we cannot know when the data are 
commented or other things happens inside the comment api. We must allow 
a callback on an event. Otherwise is impossible to know on the 
application side when a new comment s added and we cannot update stats, 
clean cache in application etc. Other implementation outside the 
callback will be confusing, hard to maintain and splitted on to many 
places.

Duck