Particle System "origin" and addParticle()

[shiffman]

#75 is now merged but one thing I want to go back and look at is how the origin is stored and intialized with a particle system. Overall I find this passing in x,y and then creating a vector more clear than passing in a vector and calling copy(). In addition, some of the example there isn't a good reason to store an origin and it would make more sense to call addParticle(x,y).

[shiffman]

Noting that I'm also going to rewrite the ParticleSystem class to be called Emitter. Starting this today.

[shiffman]

Completed