adding check_authorization and skip_authorization controller class methods to ensure authorization is triggered (thanks justinko) - closes #135

the new and create actions will now build the resource with attributes based on ability conditions hash - closes #114

passing a hash to can? will check permissions on association, this is done automatically in authorize_resource - closes #121

skip block when only class is passed to ability check, also don't pass class to block for :all - closes #116

support multiple resources in :through option of load_resource, this makes polymorphic associations possible - closes #73