Added `lifespan` argument to Particles.Arcade.Emitter.emitParticle.
Added `lifespan` argument to Particles.Arcade.Emitter.emitParticle.

This change enables a single particle to be emitted with a custom
lifespan. This adds flexiblity for users who may be using one
emitter over a big sprite sheet.

danbolt/phaser,danbolt/phaser,danbolt/phaser