Branch cleanup, move nv21 work to a staging branch

[magik6k]

• [x] Setup feat/nv21 from current master
  • https://github.com/filecoin-project/go-state-types/tree/feat/nv21
• [x] Start a revert branch
• [x] Reset to ff2ed169ff566458f2acd8b135d62e8ca27e7d0c
• [x] Cherry-pick #191
• [x] Open a PR reapplying feat/nv21 changes to the revert branch (which will become master when revert branch is merged) - https://github.com/filecoin-project/go-state-types/pull/208
• [ ] Merge the revert branch into master

[arajasek]

Hang on, I don't think we're aligned here, this seems unnecessary and bad to me. I'd like us to leave as much nv21 stuff as possible in master. Anything that is non-breaking, like the new network version, the new actor types, the migration, etc. can stay there. I think we only need to stage changes that can't currently be pulled into Lotus master because it would break things. I'm not sure what those specific changes are, but I'd like us to only revert those changes into a dedicated staging branch like feat/synth-porep or something. For all other purposes master can be the nv21 branch.

This is what we've historically done, and it's worked pretty well. From my perspective, this might only be a problem if we ever have to urgently ship a different network upgrade, and so might wind up having to revert changes. Even in that case, though, I think we'd simply force reset to the "clean" commit that adds the new types identical to the previous version (we don't have an example for v12, but here's the v11 one), and then make whatever new changes we need.

[magik6k]

After some back-and-forth it looks like we don't really need to do this, and it will be cleaner to just merge the current lotus feat/nv21 into lotus master, at which point anything else can start pulling in latest GST