Handle upstreams without a trailing slash

- Changed from using string == to hmac.Equal
- See more details here: http://verboselogging.com/2012/08/20/a-timing-attack-in-action

Pass in the original email address too as X-Forwarded-Email.

Add /ping endpoint

/v2/userinfo going away, switch to new scopes and id token payload

Make it looks a little better in mobile browsers

Fixed wrong error message

proposed LICENSE for google_auth_proxy

Update README with new Google Developers workflow

The Google Developers Console has a new interface and workflow. Updated the **OAuth Configuration** section with the correct steps, including a few notes on potential missteps.

Allow specifying multiple google apps domains.

Updated redirect arg handling to only happen when needed.

Added the ability to pass an optional redirect path as part of the manual login form

add travis badge

fix markdown syntax