Add filtering when retrieving comments and posts by user
Throw ArgumentOutOfRangeException for invalid limit
Merge pull request #59 from ianhattendorf/feat/get-filtered

Add filtering when retrieving comments and posts by user
Added sender to Comments and added const value.
Changed ushort into int
Merge pull request #60 from lieuwex/master

Added parent to Comments and made RedditUser max value to a const.