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/venusaur.asm

@@ -0,0 +1,10 @@
+; VenusaurPokedexEntry: ; 0x181773
+	db "SEED@" ; species name
+	dw 607, 2210 ; height, weight
+
+	db   "As it warms it-"
+	next "self and absorbs"
+	next "the sunlight, its"
+	page "flower petals"
+	next "release a pleasant"
+	next "fragrance.@"