message: Update CHANGELOG for proto-signing encode object
diff: @@ -73,6 +73,8 @@ and this project adheres to
  include `gasUsed` and `gasWanted` properties.
  - @cosmjs/cosmwasm-stargate: `CosmWasmClient.broadcastTx` and `.getTx` results
  now include `gasUsed` and `gasWanted` properties.
  +- @cosmjs/proto-signing: Export `DecodeObject` and `TxBodyEncodeObject`
  + interfaces as well as `isTxBodyEncodeObject` helper function.
  ### Changed
  