Read package rename options via configuration file

[mcmire]

When create-release-branch adds commits to a package's changelog, it regenerates the whole file. If the package was renamed at some point, however, the tag references at the end of the changelog will reflect the rename (that is, at some point, the tag name may change). The core repo (which has some of these types of packages, e.g. json-rpc-engine) communicates this rename to this tool (auto-changelog) by passing a couple of command-line options, --tag-prefix-before-package-rename and --version-before-package-rename. However, those options are local to core and this tool doesn't know about them when run elsewhere. So when this tool updates changelogs for those kinds of packages via create-release-branch, it resets the tag references, making them invalid from core's perspective.

Instead of receiving this information through command-line options, this tool should receive it through a configuration file. This way, whether it is run via core or create-release-branch, it always generates the right changelog.

We could read the configuration file via cosmiconfig or some other mechanism.