Support for multi white listed urls with regex url match.

Sample Command to run multi whitelisted urls with regex.

./google_auth_proxy \
  --redirect-url="http://yourcallbackurl.com/oauth2/callback"  \
  --google-apps-domain="yourdomain.com" \
  --upstream=http://127.0.0.1:8080 \
  --cookie-secret="nuts"\
  --client-id="your client id" \
  --client-secret="your client secret"  \
  --cookie-expire=0h30m0s \
  --cookie-https-only=false \
  --white-listed-urls="/hello.php","/status.php","/health-check-url/*"
I'm not sold on this naming, how about `--skip-auth-regex=...`?

The description should probably be `bypass authentication for requests path's that match (may be given multiple times)`