Bring out the horde! (v0.5)

Okay, now this is a big one. For v0.5 I've added new enemies, a new damage type system to counter said enemies, and a bunch of other smaller things. I'll get right into it!

Changelist:

• Added a damage type for each power and a resistance/weakness to each enemy;
• Changed the War Bow and Arrow Volley powers' damage type to Pierce;
• Changed the Fireball and Boiling Oil powers' damage type to Fire;
• Changed the Lightning Strike's damage type to Thunder;
• Changed the Stonewall's damage type to Earth;
• Reworked enemy: the Grunt. These are the gray boxes, the most basic enemies. They are fast but can be killed easily with a single hit from any power. Most numerous and have no special weaknesses or resistances;
  
• New enemy: the Shielder. These are the white thin boxes. These enemies appear in shield formations making them slow and nearly immune to arrows. x0.8 movement speed and 80% chance to take no damage from arrows;
• New enemy: the Battering Ram. These are the big brown boxes. They are slow (x0.5) but deal heavy damage (15) to structures. They are resistant to arrows (x0.5) but weak to Fire and Earth damage (x2);
• New enemy: the Trebuchet. These are the tall orange boxes. They are rare but can stay at range to throw boulders that deal heavy damage (30) on your castle. Destroy on sight! Like the battering ram, they are resistant to arrows (x0.5) and weak to fire (x1.5), but a lightning bolt is a certain method to destroy them (x2).
• Added a pause screen (Esc). Settings still not working, no confirmation window for the Quit button;
• Arrows now aren't balls anymore and they rotate mid-flight;
• Stonewall power now deals damage to enemies standing on top of it when it's summoned;
• Lightning Strike is now an AoE attack instead of a falling projectile;
• Fireball now explodes!
• Added a much-needed crosshair limit indicator to the Fireball, Stonewall, and Lightning Strike powers;
• Added an enemy spawner system to better control which enemy spawns when, though it might need some rework in the future for better flexibility;
• A bunch of other behind-the-scenes optimizations.

A lot of this version was dedicated to preparing the game for future features as well, such as adding sprites and animations. Each enemy already has a working state machine with empty animations so I can just plug them in and give a few adjustments when the art is ready. I'm not really happy with the enemy spawner since right now I can only spawn X type of enemy once every Y seconds, but I really wanted a system in which I could make a list of enemies and spawn each in a set amount of time, so that I can go crazy when I'm working on future levels, such as spawning 10 Grunts at 35 seconds into the level, instead of a constant stream of 1 grunt every 5 seconds. But that's not a priority right now.

Oh, and the game is obviously not balanced. I tried doing the minimum I could, but I've yet to take a proper look at the balancin. Anyway, good luck and have fun!