Changed the haiku generation algorithm slightly so that it has a higher
chance of picking a word that is in one of the selected themes instead
of the all theme. It will look through all words, but it is a 80% chance
(as of now, it is just a constant) that it will go through all the words
from the selected themes first. I didn't set it to 100% because the
haikus reused words a little too often when I tried it.