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

Move some data into a pokemon/ subdirectory

data/pokemon/dex_entries/magcargo.asm

@@ -0,0 +1,10 @@
+; MagcargoPokedexEntry: ; 0x1d0b21
+	db "LAVA@" ; species name
+	dw 207, 1210 ; height, weight
+
+	db   "Its body is as hot"
+	next "as lava and is"
+	next "always billowing."
+	page "Flames will"
+	next "occasionally burst"
+	next "from its shell.@"