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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/spinarak.asm

@@ -0,0 +1,10 @@
+; SpinarakPokedexEntry: ; 0x1cd012
+	db "STRINGSPIT@" ; species name
+	dw 108, 190 ; height, weight
+
+	db   "If prey becomes"
+	next "ensnared in its"
+	next "nest of spun"
+	page "string, it waits"
+	next "motionlessly until"
+	next "it becomes dark.@"