add gravatar support
Merge pull request #7 from lowstz/gravatar-support

Add comments Gravatar support
Updating a logging message
Updating README with latest additions
Typo
Adding contributors section on README file
Removing spaces
Adding get_template_namespace in BaseHandler
Using get_avatar from namespace on template
Adding memoized decorator for get_avatar helper
Changing function's name from get_avatar to get_gravatar_url
Group options
Improved options definition