Commits that revert other commits don't get copied into the Unreleased section #213
Description
If a changelog entry is added to the changelog in a previous release with an attached PR and then another commit is created which reverts that commit, it will not be copied to the Unreleased section. This happens because auto-changelog thinks that it's already been added (because the title of the revert commit includes the original PR number). (See example revert commit.)
Parsing the PR number out of the changelog entry would fix this. This may be related to #150 in that sense.