Add CLI options for a configuration file (-n/--config-file) and to ignore implicit configuration files (-g/--ignore-config-files).
If no explicit --config-file is specified, look for an implicit configuration file named .kiwi-changelog.yml in the current directory, then the parent directory, and finally the user's home directory.
Add ExternalChangelogConfig and ExternalCategory classes which together represent an external configuration file.
Add the ability to specify emoji for categories via CLI arguments (-e/--emoji-mapping) or via configuration file.
Add a simple MapExtensions.kt with a doesNotContainKey extension function for maps.
Modify ChangeLogFormatter.kt so that if the category order specified via -O (or --category-order) does not contain all the categories in the tickets (GitHub issues/PRs), then we print a warning to stdout, and add the missing categories. This ensures we don't produce change logs that are missing issues and/or PRs for the release/milestone.
Misc:
Add small kotlin logging library to make logging with SLF4J nicer.
Add Logback configuration files for the main and test sources.
Remove the .keep files in source and test resources since there are now files in those directories.
Misc:
Closes #31 Closes #142 Closes #143