Fix Regen Ledger lint errors and add golint CI task

[aaronc]

We want to be able to run golint ./... in CI. This mostly checks that all modules have appropriate doc strings. So this issue is mostly about adding missing source code documentation.

Definition of Done:

• you can run golint ./... from the project root and there are no errors
• there is a new CI stage that runs golint ./.... We should probably do this with https://github.com/golangci/golangci-lint instead of golint directly

[clevinson]

@aaronc should this get closed ?

[aaronc]

I think it's still relevant.

[aleem1314]

This issue addressed in this golangci-lint PR.