cloud/s3 : Added delobj command to delete objects within buckets

##### Issue Type:

Feature Pull Request

##### Ansible Version:

ansible 1.7 (s3del 337df5a648) last updated 2014/05/27 18:55:45 (GMT +000)

##### Environment:

N/A 

##### Summary:

Added delobj command to delete objects within buckets.  Note: I decided to use 'delobj' as a new command rather than overriding the existing 'delete' command.  'delete' deletes an entire bucket and all its contents.  I didn't want to risk a user deleting an entire bucket by accidentally forgetting to set the object parameter or setting it to an empty value. 

##### Steps To Reproduce:

    - s3: bucket=mybucket object=/path/to/item mode=delobj

##### Expected Results:

/path/to/item should be deleted from the specified bucket

##### Actual Results:

/path/to/item is deleted from the specified bucket