Be capable to add more attributes for profile exchange

[shawnzhu]

It only allows 4 required attributes for attribute change:

• name
• email
• first name
• last name

It should support adding more attributes. for example:

passport.use(new OpenIDStrategy({
  returnURL: 'http://www.example.com/auth/openid/return',
  realm: 'http://www.example.com/',
  profile: true,
  attributes: {"http://openid.net/schema/person/guid": "required"}
},
function(identifier, profile, done) {
  // ...
}

));