Update lib/omniauth/strategies/open_id.rb

Make creating the data hash a bit easier to understand.
add license to gemspec
Add `immediate`, `trust_root` options
Resolve root URI for `trust_root` option

Example:

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :open_id, trust_root: proc{|root_uri| "#{root_uri}sessions/"}
end