Exposes informative methods about the rating.

userHasDeclinedToRate and userHasRatedCurrentVersion
Update Appirater.h

Added a note on -(BOOL) userHasRatedCurrentVersion to clarify that this is not a guarantee that the user has actually rated the app.
Merge pull request #199 from josejulio/master

Exposes informative methods about the rating status.
Merge branch 'master' of git://github.com/arashpayan/appirater