Adapt automgtic to oauth2 realities

Adapt README to use the oauth2 URL now that mediagoblin uses to
register a new client.

Don't pull in from some oauthlib.oauth.draftXX URL, oauthlib simpliz uses
oauthlib.oauth2 now.
Merge pull request #5 from spaetz/master

Adapt automgtic to oauth2 realities