More documenting trainer hill

- Renamed members and added comments in the TrHillDisplay struct.
- Formatted the trainer hill data to better match the metatile layout its representing.
- Documented the function which uses this data.

include/trainer_hill.h

@@ -8,10 +8,10 @@ struct TrainerHillTrainer
     u8 name[HILL_TRAINER_NAME_LENGTH];
     u8 facilityClass;
     u32 unused;
-    u16 speechBefore[6];
-    u16 speechWin[6];
-    u16 speechLose[6];
-    u16 speechAfter[6];
+    u16 speechBefore[EASY_CHAT_BATTLE_WORDS_COUNT];
+    u16 speechWin[EASY_CHAT_BATTLE_WORDS_COUNT];
+    u16 speechLose[EASY_CHAT_BATTLE_WORDS_COUNT];
+    u16 speechAfter[EASY_CHAT_BATTLE_WORDS_COUNT];
     struct BattleTowerPokemon mons[PARTY_SIZE];
 };
 
@@ -23,11 +23,19 @@ struct TrHillRoomTrainers
 
 struct TrHillDisplay
 {
-    u8 data[0x100];
-    u16 unk3A0[16];
-    u8 coords[2]; // x first 4 bits, y last 4 bits
-    u8 direction; // array of 4 bits for each trainer
-    u8 range; // array of 4 bits for each trainer
+    // Metatile data. Add 0x200 to the values in this array to get metatiles. 
+    // This data then overwrites the metatiles in the map starting at (0,5)
+    u8 metatileData[0x100]; 
+    // Collision data. One bit for each tile in column-major order, 
+    // so every array entry is one row. 1 = impassable, 0 = passable
+    u16 collisionData[16];
+    // Trainer coordinates, starting at (0,6). Format is 0bYYYYXXXX.
+    u8 coords[2];
+    // Trainer facing directions. Same as (DIR_* - 1). 
+    // Effectively an array of nibbles, one for each trainer.
+    u8 direction;
+    // Trainer sight ranges. Effectively an array of nibbles, one for each trainer.
+    u8 range; 
 };
 
 struct TrHillFloor