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/entei.asm

@@ -0,0 +1,10 @@
+; EnteiPokedexEntry: ; 0x1d15dd
+	db "VOLCANO@" ; species name
+	dw 607, 4370 ; height, weight
+
+	db   "This brawny"
+	next "#MON courses"
+	next "around the earth,"
+	page "spouting flames"
+	next "hotter than a"
+	next "volcano's magma.@"