Rename all files in data/pokedex/entries/

Some people suggested this would be a good idea, and make management of
the files easier. I'm inclined to agree.

data/pokedex/entries/grimer.asm

@@ -0,0 +1,10 @@
+; GrimerPokedexEntry: ; 0x1b89a2
+	db "SLUDGE@" ; species name
+	dw 211, 660 ; height, weight
+
+	db   "When two of these"
+	next "#MON's bodies"
+	next "are combined"
+	page "together, new"
+	next "poisons are"
+	next "created.@"