To use SP metadata information for IdP configuration.

[Zogoo]

It seems like our README's sample configuration for SP makes people more confused. For example, the following questions are asked by other developers.

1. Question on configuring SP #152
2. undefined method `acs_url' for nil:NilClass #160

I have realized that if we use SP metadata for IdP configuration we can make the configuration process easier. Because, SP metadata itself must exist before SAML response gets generated (before SamlIdp.configure gets called).

[lucasocon]

+1