how to pass back the refreshed oauth2_proxy cookie from an nginx auth_request

/oauth2/auth is not more sensitive than other /oauth2/ paths,
does not need "internal" protection

"spdy" protocol is obsolete, http2 is the thing to enable now.
But it's orthogonal anyway.

No need for two separate content/upstream location blocks in
this example, reduce to just one, with a comment that it could
be serving files instead of proxying.

* This fixes https://github.com/bitly/oauth2_proxy/issues/205
* Add new boolean option -pass-user-headers
  to control whether X-Forwarded-User and X-Forwarded-Email
  headers will be set (as opposed to HTTP BASIC auth)
* This is required e.g. for grafana [1] where
  X-Forwarded-User is needed but HTTP BASIC auth fails
  (password is not known and must not be known in this scenario)
* Keep behaviour of PassBasicAuth unchanged for compatibility

[1] http://docs.grafana.org/installation/configuration/#authproxy

The correct endpoint is /oauth2/auth

* will not re-prompt if the email permission is denied, or if you previously authorized the same FB app without the email scope.

Google changed to developer console UI, updated walkthrough to match new UI.

Closes #152.

The path should be provided as a file:// url with the full operating system path.
An alias to where the directory is available as can be specified by appending
a fragment (ie. "#/static/") at the end of the URL.

By setting this to "force", certain providers, like Google,
will interject an additional prompt on every new session. With other values,
like "auto", this prompt is not forced upon the user.

*snicker*
*titter*
*giggle*

For tools that don't like empty passwords, this change allows
one to set a shared secret password for all users.

* bump version to 2.0
* remove --cookie-https-only option
* add windows build to dist.sh
* rename --cookie-key to --cookie-name