First attempt at marks support.
Remove mark inversion.

File operations need to know the path of all marked entries. But
if the marks are inverted, then paths are only available when
the file operation occurs on the same directory as the marks.
Add delete support.
Generalize file/dir processing.
Add copy support.
Add move support.
Use rename() to move files.
Use static.
Preprocessing must be applied to destination.
Erase dirpath when there are no marks.
Tag slot as free in marks.
Fix marks indices in listing.
Use diamond shape for marks.
Fix bugs caused by memory garbage.
Leave some scroll positioning to update().
Make mark symbol configurable.
Add message helper.
Avoid circular copy/move.
Move must remove source directories.
Add file/dir creation support.