Add follow camera

game.h

@@ -2,6 +2,28 @@
   game: this file implements the backend of a complete, actually playable
   game, and is meant to be included and used by specific frontends (which
   will handle each platform's hardware details and I/O).
+
+  TODO: more documentation
+
+  UNITS: There are various kinds of units used to ensure independence of the
+  game modules. Here is a summary:
+
+  - LCR_GameUnit: data type, abstract unit of the game (racing module). One map
+    square is LCR_GAME_UNITs long, a full angle is also LCR_GAME_UNITs.
+  - LCR_GAME_UNIT: Size of one game square and full angle in LCR_GameUnits.
+  - S3L_Unit: data type, small3dlib's unit. May change with renderer change.
+  - S3L_FRACTIONS_PER_UNIT: small3dlib's value representing 1.0.
+  - LCR_RENDERER_UNIT: for the renderer one map square is this many S3L_Units.
+  - TPE_Unit: tinyphysicsengine's unit. May change with phys. engine change.
+  - TPE_FRACTIONS_PER_UNIT: tinyphysicsengine's value representing value 1.0.
+  - LCR_PHYSICS_UNIT: for the phys. eng. one map square is this many TPE_Units.
+
+  COORDINATE SYSTEM AND ROTATIONS: The game itself (racing module) is
+  independent of rendering and physics libraries, but out of convenient adopts
+  their coordinate system (X right, Y up, Z forward) and rotations (Euler
+  angles, by Z, then by X, then Y). 
+
+
 */
 
 #ifndef _LCR_GAME_H