Clean up CLI flags and README
Fix missing usage details in CLI, rework the shorthand flag names,
adjust README and add checks to sub-commands to have the right
number of arguments. Harmonize the wording in the usage and help
texts.
Switch color definition
Change custom color definition in favor for colorful package. This
includes a improved diff output with more color differences and indent
guide lines.
Add special minor change use case
The percent threshold naturally does not work well for short strings.
For use cases where only two characters are changes, condider it a
minor change, too.