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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/seadra.asm

@@ -0,0 +1,10 @@
+; SeadraPokedexEntry: ; 0x1b95b8
+	db "DRAGON@" ; species name
+	dw 311, 550 ; height, weight
+
+	db   "The male raises"
+	next "the young. If it"
+	next "is approached, it"
+	page "uses its toxic"
+	next "spikes to fend off"
+	next "the intruder.@"