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/mankey.asm

@@ -0,0 +1,10 @@
+; MankeyPokedexEntry: ; 0x182dbd
+	db "PIG MONKEY@" ; species name
+	dw 108, 620 ; height, weight
+
+	db   "It lives in groups"
+	next "in the treetops."
+	next "If it loses sight"
+	page "of its group, it"
+	next "becomes infuriated"
+	next "by its loneliness.@"