Move trade data, some trade.c clean up documentation

include/constants/trade.h

@@ -0,0 +1,13 @@
+#ifndef GUARD_CONSTANTS_TRADE_H
+#define GUARD_CONSTANTS_TRADE_H
+
+#define TRADE_PLAYER  0
+#define TRADE_PARTNER 1
+#define TRADE_PARTICIPANT_COUNT 2
+
+#define INGAME_TRADE_SEEDOT 0
+#define INGAME_TRADE_PLUSLE 1
+#define INGAME_TRADE_HORSEA 2
+#define INGAME_TRADE_MEOWTH 3
+
+#endif //GUARD_CONSTANTS_TRADE_H