oauth2: fix lint errors

Change-Id: I9cc4c61767be5e6eda189468430e9a89fe2f3796
oauth2: redesign the API

Tests and examples aren't updated yet. The tree will be broken after this,
but nobody should be using this yet anyway.

Change-Id: I0004c738f40919ab46d107c71c011c510fbc748f
Reviewed-on: https://go-review.googlesource.com/1246
Reviewed-by: Burcu Dogan <jbd@google.com>
oauth2: rewrite google package, fix the broken build

Change-Id: I2753a88d7be483bdbc0cac09a1beccc4806ea4bc
Reviewed-on: https://go-review.googlesource.com/1361
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>
github: new package with Github's Endpoint

Change-Id: I4a64493f521678570a89d5da76604c258fb9ceac
Reviewed-on: https://go-review.googlesource.com/1631
Reviewed-by: Andrew Gerrand <adg@golang.org>