gh2md --multiple-files should produce canonical file paths

[milahu]

actual

2020-11-04.3.issue.closed.md
2022-07-09.24.issue.open.md

problem: closed and open are not "canonical" but variable this means issue urls are not permalinks, and git history is broken at file renames

expected

2020-11-04.3.issue.md
2022-07-09.24.issue.md

or

issues/3.md
issues/24.md