Refresh man pages

- Fix name of man pages for all but the toplevel command
- Set title of all man pages to "GitHub CLI manual"
- Include gh version information in man pages
- Clean up rendering of flags section
- List subcommands for every command

.goreleaser.yml

@@ -8,7 +8,7 @@ release:
 before:
   hooks:
     - go mod tidy
-    - make manpages
+    - make manpages GH_VERSION={{.Version}}
 
 builds:
   - <<: &build_defaults