Implement unicorn spawning
Implement Unicorn gravity and collision.

Collision detection misses enemies sometimes.
Improve Unicorn hit detection
Remove Unicorn Debugging
Add composite ParticleEffects.

The old "ParticleEffect" is now called a ParticleGenerator.
The new "ParticleEffect" is a composite of 1 or more ParticleGenerators.

Instantiate a ParticleGenerator just like a ParticleEffect by passing in a
string that references an entry in ParticleEffects.xml.
If an entry for such an effect exists, it will instantiate an effect
containing all the defined generators.
If no such ParticleEffect exists, it will search for a ParticleGenerator
with the same name, and instantiate a ParticleEffect with only that one
generator (in other words, all the old particle effects now work as a
ParticleEffect wrapped around a single generator).
Improve flexibility of particle effect creation

A particle effect is, as before, defined as a collection of one or more
particle generators. However, one may now override individual attributes
of particle generators in their instantiation in a particle effect.

For example, the particle effect xml element:

<ParticleEffectData Name="MyParticleEffect">
	<ParticleGenerator Name="Effect1" StartColor="255,255,0,0"/>
	<ParticleGenerator Name="Effect1" StartColor="255,0,255,0"/>
	<ParticleGenerator Name="Effect1" StartColor="255,0,0,255"/>
</ParticleEffectData>

creates a particle effect consisting of three instances of Effect1, each
with a different start color.
Add generator offsets in ParticleEffects
Improve Unicorn Particle Effect
Improve particle effect loading
improve blackhole and unicorn effects
Further improve particle effects
Merge remote-tracking branch 'kalgynirae/master'
Remove GameStateDrawMenu.cs
Improve Unicorn behavior.

Unicorn now rotates, scanning for player.
When player is found (falls within unicorn cone of vision) there is a
brief delay before unicorn charges.
Implement food cart.

Shop state is not complete yet, so there is no logic for entering the
shop. This just implements basic spawning, movement, and collision
detection for food carts, as well as the ability to include them in levels
by adding elements to a level in leveldata.xml.
Add transparency to the Spaceman spritesheet