Git commit message linter

[vemv]

Context

Certain commit messages can be dangerous (fixes #7 lacks a namespace, can close unreated issues if the commit is moved to a new repo) simply not that recommended.

Task

Create a linter that analyzes the git log output.

Acceptance criteria

• The git log is only examined under certain circumstances, so that f-s doesn't pester the user about already-accepted commits.

A simple starting point would be to only add the linter to the formatting-stack.branch-formatter ns.