Split items/ and trainers/ into their data/ and engine/ components

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/magmar.asm

@@ -0,0 +1,10 @@
+; MagmarPokedexEntry: ; 0x1b9994
+	db "SPITFIRE@" ; species name
+	dw 403, 980 ; height, weight
+
+	db   "It moves more"
+	next "frequently in hot"
+	next "areas. It can heal"
+	page "itself by dipping"
+	next "its wound into"
+	next "lava.@"