changelog: alligator arena, documentation and known limits for 0.2.1; current launcher and editor screenshots everywhere, coaster in the readme pictures

CHANGELOG.md

@@ -40,6 +40,10 @@ There are two downloads: **full** (launcher + level editor) and **launcher** (mo
     Boot to level) no longer damages your progress.
   - The level tally shows the real coin and secret totals of new levels, the Test World and the
     arena instead of the Village's "55".
+  - **New: Alligator Arena** – a minigame on a TestLevel chapter (default 49): alligators come in
+    waves into a walled pit; every hit costs one of their lives and coins pop out, their bite
+    costs your energy; beat every wave and the exit opens. Lives, waves, energy and coins per hit
+    can be set.
   - **New: Llama Coaster** – a roller-coaster ride on a TestLevel chapter (default 48), with the
     cart from the Catacombs: drops, climbs, boost arrows, a jump and a spin pad. Two tracks, 1–3
     laps, three speeds.
@@ -81,7 +85,15 @@ There are two downloads: **full** (launcher + level editor) and **launcher** (mo
   - Opcodes have checked descriptions.
 - Narrow docks, small windows and long labels wrap instead of being cut off.
 
+### Documentation
+
+- New guide for building your own levels, a reference of the game's file formats and engine
+  limits, and a chapter on object scripts (strats) with the arena and the coaster as worked
+  examples: start at [docs/README.md](docs/README.md).
+
 ### Known limits
 
 - Tested on Linux (Wine) and in a Windows VM. Real Windows hardware is not tested yet.
 - The game draws objects only within about 12 units of the llama.
+- Four music tracks of the game have no file on the CD (GAMEOVER, TALLY, PUZZLE2, PLATFORM); the
+  editor marks them.