Allow checking an array of groups for Sentry::user()->in_group().

For example:
Sentry::user()->in_group('Admin');
Sentry::user()->in_group(1);
Sentry::user()->in_group(array('Admin', 'Owner', 'Client'));
Sentry::user()->in_group(array(1, 3, 8));
fix issue with remove_from_group not actually removing from group
Merge pull request #61 from mike182uk/develop

Remove from group not actually removing from group
Fixed update method to allow for updating of username when login column equals 'email'
Merge pull request #69 from michaeldim/develop

Fix update method to allow for updating of username when login column == 'email'
updating a docblock
added lang var needed from last pull request
Comment correction to update method
Merge pull request #70 from michaeldim/develop

Comment correction to update method for username field
Update classes/sentry/attempts.php
Merge pull request #39 from danharper/patch-2

Allow checking an array of groups for Sentry::user()->in_group()
Merge branch 'refs/heads/fuelphp/develop' into fuelphp/master