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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/heracross.asm

@@ -0,0 +1,10 @@
+; HeracrossPokedexEntry: ; 0x1d0907
+	db "SINGLEHORN@" ; species name
+	dw 411, 1190 ; height, weight
+
+	db   "With its Herculean"
+	next "powers, it can"
+	next "easily throw arou-"
+	page "nd an object that"
+	next "is 100 times its"
+	next "own weight.@"