message: Fix and improve MIGRATING text
diff: @@ -232,7 +232,7 @@ major releases of `cosmwasm`. Note that you can also view the
  deserialization. In order to maintain type safety, deserialization into `Addr`
  must only be done from trusted sources like a contract's state or a query
  response. User inputs must be deserialized into `String`. This new `Addr` type
  - allows makes it easy to use human readable addresses in state:
  + makes it easy to use human readable addresses in state:
  With pre-validated `Addr` from `MessageInfo`:
  @@ -243,7 +243,7 @@ major releases of `cosmwasm`. Note that you can also view the
  }
  let state = State {
  - owner: deps.api.canonical_address(&info.sender)?,
  + owner: deps.api.canonical_address(&info.sender /* of type HumanAddr */)?,
  };
  @@ -252,7 +252,7 @@ major releases of `cosmwasm`. Note that you can also view the
  pub owner: Addr,
  }
  let state = State {
  - owner: info.sender.clone(),
  + owner: info.sender.clone() /* of type Addr */,
  };
  ```
  @@ -269,9 +269,9 @@ major releases of `cosmwasm`. Note that you can also view the
  deps.storage.set(
  CONFIG_KEY,
  &to_vec(&State {
  - verifier: deps.api.canonical_address(&msg.verifier)?,
  - beneficiary: deps.api.canonical_address(&msg.beneficiary)?,
  - funder: deps.api.canonical_address(&info.sender)?,
  + verifier: deps.api.canonical_address(&msg.verifier /* of type HumanAddr */)?,
  + beneficiary: deps.api.canonical_address(&msg.beneficiary /* of type HumanAddr */)?,
  + funder: deps.api.canonical_address(&info.sender /* of type HumanAddr */)?,
  })?,
  );
  @@ -285,16 +285,16 @@ major releases of `cosmwasm`. Note that you can also view the
  deps.storage.set(
  CONFIG_KEY,
  &to_vec(&State {
  - verifier: deps.api.addr_validate(&msg.verifier)?,
  - verifier: deps.api.addr_validate(&msg.verifier)?,
  - funder: info.sender,
  + verifier: deps.api.addr_validate(&msg.verifier /* of type String */)?,
  + beneficiary: deps.api.addr_validate(&msg.beneficiary /* of type String */)?,
  + funder: info.sender /* of type Addr */,
  })?,
  );
  ```
  - The existing `CanonicalAddr` remains unchanged and can be used in which a
  - compact binary representation is desired. For JSON state this does not save
  - much data (e.g. the bech32 address
  + The existing `CanonicalAddr` remains unchanged and can be used in cases in
  + which a compact binary representation is desired. For JSON state this does not
  + save much data (e.g. the bech32 address
  cosmos1pfq05em6sfkls66ut4m2257p7qwlk448h8mysz takes 45 bytes as direct ASCII
  and 28 bytes when its canonical representation is base64 encoded). For fixed
  length database keys `CanonicalAddr` remains handy though.
  