TODO

- Add GitHub Auth when downloading source for verification.
  - If GITHUB_TOKEN is set, always use it.
  - Add help text to error when auth is needed but not provided.
- Install needed Go version if not already present on system.
- Add a shim so that 'go' for the build is the correct go version.
- Move config package to pkg/
- Extract Product package to its own place for import by other products.


- Change CLI:

	actions-go-build build              (build current dir)
	actions-go-build build .            (build current dir)
	actions-go-build build some/dir/    (build some/dir/)
	actions-go-build build buildresult.json        (remote verification build)
	actions-go-build build verificationresult.json (remote verification build)
	actions-go-build build http://xyx/result.json  (remote verification build)

	actions-go-build verify             (local verification build, current dir)
	actions-go-build verify .           (local verification build, current dir)
	actions-go-build verify some/dir/   (local verification build some/dir/)
	actions-go-build verify buildresult.json        (remote verification result)
	actions-go-build verify verificationresult.json (remote verification result)
	actions-go-build verify http://xyx/result.json  (remote verification result)
	actions-go-build inspect [-env] [-describe-env] [-cache] [build-ish] 
		- Print build env, cache status of various results.

	actions-go-build build-env -describe
	actions-go-build build-env                          (build env current dir)
	actions-go-build build-env .                        (build env current dir)
	actions-go-build build-env some/dir/                (build env some dir)
	actions-go-build build-env buildresult.json         (build env for that result)
	actions-go-build build-env verificationresult.json  (build env for that result)
	actions-go-build build-env http://xyx/result.json   (build env for that result)
	actions-go-build config           [configish]
	actions-go-build config -export   [configish]


[build-ish] is anything that could be considered a build, e.g. a directory containing
  source code, a path or URL to a buildresult, a verificationresult etc.

[source-tree] is a directory containing source code.