Particles on collide

Nothing major, same particle system, just hooked into the collision system.  Only update needed was passing along the collision point into the resolution system.  Improves the "run into stuff" upgrade. 

It's now overpowered... i gave 5x starting hp so that you can collect a few minions before running out of hp.  Feel like this would be tricky to balance long term.  But with the second upgrade, getting the explosion is fun, tag something then pile drive into it to make an explosion!