revert palette and alpha after parsing

This avoids having to do it each time you use it.
Warning: breaking change

src/vobsub/sub.rs

@@ -14,6 +14,7 @@ use crate::{
     },
 };
 use cast;
+use iter_fixed::IntoIteratorFixed;
 use log::{trace, warn};
 use nom::{
     bits::{bits, complete::take as take_bits},
@@ -408,6 +409,9 @@ where
     //
 
     let end = cast::usize(initial_control_offset + 2);
+    // reverse palette & alpha once for all
+    let palette = palette.into_iter_fixed().rev().collect();
+    let alpha = alpha.into_iter_fixed().rev().collect();
     let image_data = VobSubRleImageData::new(raw_data, rle_offsets, end)?;
     let rle_image = VobSubRleImage::new(area, palette, alpha, image_data);
 
@@ -614,8 +618,8 @@ mod tests {
             })
             .unwrap()
         );
-        assert_eq!(*sub1.image.palette(), [0, 3, 1, 0]);
-        assert_eq!(*sub1.image.alpha(), [15, 15, 15, 0]);
+        assert_eq!(*sub1.image.palette(), [0, 1, 3, 0]);
+        assert_eq!(*sub1.image.alpha(), [0, 15, 15, 15]);
         subs.next().expect("missing sub 2").unwrap();
         assert!(subs.next().is_none());
     }