when generating url, model class name should be underscored
downcasing it will result in namespaced model generating invalid uri
e.g : namespace::model
fixed broken spec, undefined method 'underscore' for :file:Symbol
add spec for Namespace::Model#url
Merge pull request #12 from ignatiusreza/bug/support_namespaced_model

when generating url, model class name should be underscored