Also
- init substructures to avoid panic in pb2tm.ConsensusParams
Before: if csp.Block is nil and we later try to access/write to it,
we'll panic.
After: if csp.Block is nil and we later try to access/write to it,
there'll be no panic.
* make BlockTimeIota a consensus parameter, not a locally configurable option
Refs #2920
* make TimeIota int64 ms
Refs #2920
* update Gopkg.toml
* fixes after Ethan's review
* fix TestRemoteSignerProposalSigningFailed
* update changelog
* types: add Version to Header
* abci: add Version to Header
* state: add Version to State
* node: check software and state protocol versions match
* update changelog
* docs/spec: update for versions
* state: more tests
* remove TODOs
* remove empty test
* better overview section
* section on tags
* remove notes about state/concurrency from CheckTx
* incorporate feedback from #2249
* explain how validator set updates effect future blocks