draw particles in a batch for improved performance
changed particles to apply forces independent from the current frame
rate.
replaced all tabs with spaces.
fixed inViewport of particles not being set correctly
inlined overlap check for better performance
put draw code back into particle class
simplified particle draw method by making use of matrix2d
simplified particle update method for better readability and performance
added new parameter to particle emitter to allow for skipping updates
just splice dead particles out, as it is much faster
extend particle emitter from objectContainer
added mouse controls to particle example
added code to let particles flow in screen space (floating)
updated example with checkbox for the floating flag
fixed wrong usage of floating property
use set instead of setScale (which will not make it into matrix2d)
extracted ParticleContainer from ParticleEmitter
removed startPos and varPos in favor of emitter bounds
fixed inViewport not being set correctly
use particle.pos instead of particle.transform for position
use textureAdditive directly