Added 'accept an answer' comment

Added 'accept an answer' comment. It `@` tags the OP. It has a `[type here]` area where you can put "my", "a", "this" or another word in order to allow it to as a comment on the question or an answer.

Example:

@[OP]: If [type here] answer solved your problem, then you should accept it by clicking the checkmark on the answer. This will mark your question as answered, see more on accepting at the [help center](http://$SITEURL$/help/accepted-answer).
Made message nicer

Message mostly taken from here: http://stackapps.com/a/3584/22281
Merge pull request #45 from minerz029/patch-2

Added 'accept an answer' comment