Updated the Hashtable-Provider for more flexibility 

Added the feature to customize the array-format optionally. e.g. this will now work too: array('username' => array('password' => 'coolpw', 'email' => 'a@b.com'))
Fix bug in the hashtable provider

Fix bug: check whether $this->users[$username] is an array
Merge pull request #10 from spu95/develop

Updated the Hashtable-Provider for more flexibility