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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/mew.asm

@@ -0,0 +1,10 @@
+; MewPokedexEntry: ; 0x1cc915
+	db "NEW SPECIE@" ; species name
+	dw 104, 90 ; height, weight
+
+	db   "Because it can"
+	next "learn any move,"
+	next "some people began"
+	page "research to see if"
+	next "it is the ancestor"
+	next "of all #MON.@"