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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/exeggcute.asm

@@ -0,0 +1,10 @@
+; ExeggcutePokedexEntry: ; 0x1b8f84
+	db "EGG@" ; species name
+	dw 104, 60 ; height, weight
+
+	db   "If even one is"
+	next "separated from the"
+	next "group, the energy"
+	page "bond between the"
+	next "six will make them"
+	next "rejoin instantly.@"