Don't give away your consumer key.

When generating the authorization URL, we shouldn't give away the
application's uniq consumer key.

Additionally, make redirect_uri a client-level configuration. It is
just-as-static as consumer key, so we shouldn't have to have it
replicated multiple times when using the pocket-ruby client.
Cleanup
Merge pull request #12 from danott/security

redirect_uri included as default. removed consumer_key from authorized_url.