Renamed UrlValidator to AddressableUrlValidator to avoid 'url:' naming collision with ActiveModel::Validations::UrlValidator in 'validates' statement.
Make use of the options attribute of the parent class ActiveModel::EachValidator.
Add more options: allow_nil, allow_blank, message.
Renamed 'protocols' option to 'schemes' to match the option naming from UrlValidator.
Updates specs to use new rails5 format.
The old format:
`get :show, { some: params }, { some: headers }`
The new format:
`get :show, params: { some: params }, headers: { some: headers }`