Add 'not implemented' errors for unimplemented flags

These used to live in TODO but we got rid off them.  Make sure
we keep track of what we want to support by printing a message
when those flags are unimplemented.

sha1sum.c

@@ -17,7 +17,7 @@ struct crypt_ops sha1_ops = {
 static void
 usage(void)
 {
-	eprintf("usage: %s [file...]\n", argv0);
+	eprintf("usage: %s [-c] [file...]\n", argv0);
 }
 
 int
@@ -27,6 +27,8 @@ main(int argc, char *argv[])
 	uint8_t md[SHA1_DIGEST_LENGTH];
 
 	ARGBEGIN {
+	case 'c':
+		eprintf("not implemented\n");
 	default:
 		usage();
 	} ARGEND;