note Go >=1.1 requirement
add a slim CONTRIBUTING.md
update secureheader to fix redirect
require DATABASE_URL from hkdist web
Change `hk list` to `hk apps` in dev instructions

- `hk list` is no longer an available command; `hk apps` is the same
use identity oauth tokens for build system
Get v3 account info using OAuth identity token
use jsonsha struct

Avoid the duplication of multiple identical anonymous structs just for
encoding/decoding the sha256.
standardize hkdist paths, struct usage
fix URL for setCurVersion
use go-update, and other update cleanup

Make builds not named "hk" work successfully with updates, such as
staging builds named "hkstaging"