Implemented the GetPrivateMessages method partially in the user class for retrieving all private messages that were stored in the inbox folder
Added additional constructors for post, message and private message classes to enable assigning a date and time for created messages
The GetPrivateMessages function now also retrieves messages that haven't been read yet for the first time
Implemented paging and certain criterias that can be used for looking up private messages. Specifiying folders is also possible.
Merge pull request #4 from Mostey/user_private_messages

Retrieving Private Messages