Add /healthcheck handler to API
gofmt fixes
Merge remote-tracking branch 'origin/healthcheck'
Add Jenkins scripts
Merge pull request #6 from alphagov/jenkins-builders

Add Jenkins scripts
Fix Jenkins bash shebang
Add HTTP referrer logging

As requested by the search term, they want to see what the URL the hit
came from.
Merge pull request #7 from alphagov/log-http-referer

Add HTTP referrer logging
Add support for zero-downtime restart
vendorise upgradeable_http