feat(cli): parse -y/--fuzzy and --no-fuzzy

Register --fuzzy (alias -y) as a boolean option and fuzzy as negatable so
--no-fuzzy works through the generic negation machinery.  FastSync's delta
machinery is off by default (unlike rsync, where --fuzzy implies nothing
because delta is the default), so --fuzzy implies --incremental and --delta
unless --whole-file or an explicit --no-delta switched delta off (leaving
fuzzy inert, matching rsync where -W makes fuzzy irrelevant).  Add help text.

src/client/usage.c

@@ -81,6 +81,11 @@ void print_usage(void) {
          "used)\n");
   printf("  --delta             Delta transfer for changed files (requires --incremental)\n");
   printf("  -W, --whole-file    Transfer changed files without delta processing\n");
+  printf("  -y, --fuzzy         Use a similar-named file already in the destination\n");
+  printf("                    directory as the delta basis when the destination has no\n");
+  printf("                    usable file at the exact path (saves bandwidth; implies\n");
+  printf("                    --incremental and --delta; inert with --whole-file)\n");
+  printf("  --no-fuzzy          Disable --fuzzy\n");
   printf("  --delta-block <n>   Delta block size in bytes (default: %d)\n",
          DELTA_BLOCK_SIZE_DEFAULT);
   printf("  --delta-max <n>     Max file size for delta transfer (default: %llu)\n",