Add support to "gshred" and "rm -P" to safely delete a file

Add support to "gshred" and "rm -P" to safely delete a file

gshred(1) is shred(1) from GNU coreutils on OpenBSD

rm(1) on OpenBSD
-P      Overwrite regular files before deleting them.  Files are
        overwritten once with a random pattern.  Files with multiple
        links will be unlinked but not overwritten.