using class(es) instead of object(s) where appropriate

With reference to [Sandi Metz rules for developers](http://robots.thoughtbot.com/sandi-metz-rules-for-developers) and since [single responsibility principle](http://en.wikipedia.org/wiki/Single_responsibility_principle) sounds more appropriate when referred to a class as a whole, thus making appropriate changes. 

Please feel free to let me know your thoughts on this in case you think I'm missing something or I need to incorporate something else.

Thanks.
@gabebw I actually modified the phrasing based on @mcmire's suggestion to maintain uniformity of using the word class wherever appropriate like how I've made use of the same in my [first commit](https://github.com/boddhisattva/guides/commit/90a589f4b08ddd7b8eb24be7e2845a310b1fd87b) of this pull request . I leave it to you guys to take a final call on this, for me both works but I'd prefer the modified one(using class for uniformity sake).