Add the ability to disable saving preview images. Also rename --gamma_correct to --gamma-correct for consistency

convert.py

@@ -323,13 +323,17 @@ def main():
         '--verbose', action=argparse.BooleanOptionalAction,
         default=False, help="Show progress during conversion")
     parser.add_argument(
-        '--gamma_correct', type=float, default=2.4,
+        '--gamma-correct', type=float, default=2.4,
         help='Gamma-correct image by this value (default: 2.4)'
     )
     parser.add_argument(
-        '--fixed_colours', type=int, default=0,
+        '--fixed-colours', type=int, default=0,
         help='How many colours to fix as identical across all 16 SHR palettes'
     )
+    parser.add_argument(
+        '--save-preview', type=bool, default=True,
+        help='Whether to save a .PNG rendering of the output image'
+    )
     args = parser.parse_args()
     if args.lookahead < 1:
         parser.error('--lookahead must be at least 1')
@@ -424,6 +428,8 @@ def main():
         print("%d unique colours" % unique_colours)
 
         seq += 1
+
+        if args.save_preview:
             # Save Double hi-res image
             outfile = os.path.join(
                 os.path.splitext(args.output)[0] + "-%d-preview.png" % seq)