Big Update

Well, it's been a month, but there's a lot of content that got added.

We went from 4 levels to 15.  So there's pretty much a "full" game as far as length is concerned.  I need input if folks feel that's too long or what.

List of things added:

• Added a bunch of levels to go from a length of 4 levels to 15.  Note that right now you get to choose between 2 levels at each "step" which is why I added more than just 11 levels.  (More like 20?)
• Interest earned between each wave will slowly go down.  So the clock is ticking
• Added a bunch of upgrades for Turrets and Powers (call-downs?) as well as general interest- or node-related upgrades.
• There's probably more.  I need to be better on this changelog thing, but I didn't anticipate things taking this long.

The whole thing needs some balancing.  So let me know what feels good, what feels like it needs to be nerfed/buffed/whatever.  Thanks!

Todo: 

• Build a tutorial level at the beginning
• Change the upgrades into images and not just text
• Clear up a small thing with the turret shop and having insufficient energy to purchase something
• Unify enemy damage (back end)