Filenames with spaces; output beside the input file; warning fixes (from dev c08eb1bbfa4c)

- Filenames may contain spaces: quote on the command line; filename
  lists use a standalone "/" separator; unseparated names that do not
  exist are rejoined into names that do (announced); leading ~ expands.
- Without -o, output is written to the input file's directory; -o fully
  specifies the output directory and basename.
- "Word not parsed" warnings now appear without -v, only for text that
  survives removal, with correct line numbers.
- New tst/filename_test.sh regression suite.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -39,7 +39,7 @@ are regenerated on each release — patches cannot be merged directly.
 Report problems (or send patches) to the author; accepted changes are
 applied to the development tree and appear in a following snapshot.
 
-This snapshot was assembled from development commit `f6463478da4c`.
+This snapshot was assembled from development commit `c08eb1bbfa4c`.
 
 ## License