README.md
Updated details to say rails 4 and information on how to configure for strong parameters in rails 4

lib/devise_yubikey_database_authenticatable/strategy.rb
When using yubikey OR (not AND) a password, needed to remove the resource = valid_password?
and also change the resource.valid_password?(password) after validate(resource)
since the password may be blank if using the Yubikey only for auth

Signed-off-by: David M. Zendzian <dmz@bidadollar.com>