Add the contents of disk 1

- LHA -lh5/-lh6/-lh7 decoding with CRC checks (disk 1 is mostly lh5)
- Real track palettes and set names, read from each track file's header
- Camaro, plus the caravan as a towable trailer (Caravans option)
- Drivers' names, menu pictures and the original .set values per car
- Original sound effects (IFF 8SVX) through a new sample mixer: engine
  pitched with revs, tyre screech, crashes, backfire, horn, start beeps
- The original tune (OctaMED MMD1) through a new player; loudness tracks
  OpenMPT's render through the whole song. Music option in the menu
- Title picture (IFF ILBM) at the top of the menu
- skids unpack and skids music commands
- Gate crossings now judged on each car's whole movement per frame,
  including collision knocks; stalled computer cars are put back on the
  line after 8 seconds

The executable's game logic (handling, AI) is still not decoded.

src/data/palette.rs

@@ -1,10 +1,8 @@
 //! Colour palettes.
 //!
-//! The track and vehicle files carry no colour tables; the retail game sets
-//! them from its main executable, which lives on disk 1. Until that disk is
-//! available we use a reconstructed palette. Indices on the retail tracks are
-//! ordered dark-to-light, with 0-7 used for scenery and 8-15 for the driving
-//! surface, so two ramps give a faithful-looking result.
+//! Each original track file carries the 16-colour palette its six tracks
+//! share (see `track.rs`). `TRACK_DEFAULT` is only a fallback for track
+//! pictures that arrive without one: indices 0-7 scenery, 8-15 road.
 //!
 //! Each track asset's PNG carries its own palette, so the usual way to
 //! recolour a track is to edit that. Palettes can also be dropped in as text