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/venonat.asm

@@ -0,0 +1,10 @@
+; VenonatPokedexEntry: ; 0x182a53
+	db "INSECT@" ; species name
+	dw 303, 660 ; height, weight
+
+	db   "The small bugs it"
+	next "eats appear only"
+	next "at night, so it"
+	page "sleeps in a hole"
+	next "in a tree until"
+	next "night falls.@"