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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/charizard.asm

@@ -0,0 +1,10 @@
+; CharizardPokedexEntry: ; 0x1818b3
+	db "FLAME@" ; species name
+	dw 507, 2000 ; height, weight
+
+	db   "It uses its wings"
+	next "to fly high. The"
+	next "temperature of its"
+	page "fire increases as"
+	next "it gains exper-"
+	next "ience in battle.@"