ADR-016: Add versions to Block and State (#2644)

* 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

docs/spec/blockchain/blockchain.md

@@ -8,6 +8,7 @@ The Tendermint blockchains consists of a short list of basic data types:
 
 - `Block`
 - `Header`
+- `Version`
 - `BlockID`
 - `Time`
 - `Data` (for transactions)
@@ -38,6 +39,7 @@ the data in the current block, the previous block, and the results returned by t
 ```go
 type Header struct {
 	// basic block info
+	Version  Version
 	ChainID  string
 	Height   int64
 	Time     Time
@@ -65,6 +67,19 @@ type Header struct {
 
 Further details on each of these fields is described below.
 
+## Version
+
+The `Version` contains the protocol version for the blockchain and the
+application as two `uint64` values:
+
+```go
+type Version struct {
+    Block   uint64
+    App     uint64
+}
+```
+
+
 ## BlockID
 
 The `BlockID` contains two distinct Merkle roots of the block.
@@ -200,6 +215,15 @@ See [here](https://github.com/tendermint/tendermint/blob/master/docs/spec/blockc
 
 A Header is valid if its corresponding fields are valid.
 
+### Version
+
+```
+block.Version.Block == state.Version.Block
+block.Version.App == state.Version.App
+```
+
+The block version must match the state version.
+
 ### ChainID
 
 ```