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/arbok.asm

@@ -0,0 +1,10 @@
+; ArbokPokedexEntry: ; 0x18203d
+	db "COBRA@" ; species name
+	dw 1106, 1430 ; height, weight
+
+	db   "To intimidate"
+	next "foes, it spreads"
+	next "its chest wide and"
+	page "makes eerie sounds"
+	next "by expelling air"
+	next "from its mouth.@"