v0.1.4 - Tactical structure placement

This update is part of the first few steps to making structure placement more meaningful. 

Revamped enemy spawning

Each lane will now have different enemy distributions. This information is not given to the player but can be deduced by observing the types of enemies seen in each lane. In effect, each lane can be specialized to deal with a certain combination of enemies.

However, the implementation is very basic. Once you figure it out, you pretty much solved the puzzle. It does not change, and over all, very predictable (once you play a few times). I need to flesh this out more but for now, it should be fine for the first 5 minutes of gameplay.

Added ability to swap structures (replaced structure removal)

Due to the changes to enemy spawning, having the ability to move structures is essential. Optimizing a lane setup relies on being able to correctly assess the enemy composition. The first minute of the game doesn't really show the types of enemies you will encounter. The player's tower placement in that time will most likely be sub-optimal.

There are a few ways to abuse use this mechanic. Also note that it can be used to move structure alone.

What next?

I'm planning to change the way upgrades work. As of right now, structure upgrades are mostly stat increases. Pretty boring imho. I have a few ideas on how to make them more impactful but it would probably take more work than the last few updates I've done.