Rewrites a CHANGELOG entry.

The entry is basically copy & paste of the commit message, but the CHANGELOG
has a different purpose than Git history, it just communicates what is new:

* No need to explain why did the bug happen (unless it is truly relevant).

* No need to explain how was the bug fixed.

* Whether the user gives new names to columns does not really matter, use of
  select to cherry-pick a column for example also presented that behaviour.
  Non-selected attributes are the key, either because they were not included
  in the selected list, or because they were but with a different alias.

* In the case of an attribute alias, what you really want to depict is that
  respond_to? returns false for the original attribute name.