Balancing update

Planning a small balancing update later today:

• Combos will be nerfed. They break after 2.5 seconds instead of 3, and they will also break if you get hit. Dorothy's dialogue is changed to reflect that.
• The default difficulty setting is now 3.  I added the difficulty before adding the combo/charge mechanics, so 1 is significantly easier now. You can change it back to 1 in the settings. 
• Poison now reduces your HP based on the poison amount instead of a fixed amount.
• The weapon Pestilence now heals you if you are poisoned.

The update is out now.