message: Add CHANGELOG entry for canonicalize_address/humanize_address signature change
diff: contract. A standard library should ensure this never happens by correctly
  encoding string input values.
  - Merge trait `ReadonlyStorage` into `Storage`.
  +- The imports `canonicalize_address` and `humanize_address` now return a memory
  + address to an error `Region`. If this address is 0, the call succeeded.
  ## 0.8.1 (2020-06-08)
  