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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/ivysaur.asm

@@ -0,0 +1,10 @@
+; IvysaurPokedexEntry: ; 0x181702
+	db "SEED@" ; species name
+	dw 303, 290 ; height, weight
+
+	db   "The bulb on its"
+	next "back grows as it"
+	next "absorbs nutrients."
+	page "The bulb gives off"
+	next "a pleasant aroma"
+	next "when it blooms.@"