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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/kadabra.asm

@@ -0,0 +1,10 @@
+; KadabraPokedexEntry: ; 0x18313c
+	db "PSI@" ; species name
+	dw 403, 1250 ; height, weight
+
+	db   "When it closes its"
+	next "eyes, twice as"
+	next "many alpha parti-"
+	page "cles come out of"
+	next "the surface of its"
+	next "body.@"