Minor addition to useful utils.txt
Made it so that simple particle system coloured particles' colour channels are clamped, not cyclical.
For example, this means that a particle with an alpha of 200 and an alpha_delta of 25 has, over five frames, [200, 225, 250, 255, 255]. This is opposed to the old way, where the alpha values over five frames would be [200, 225, 250, 20, 45].
This was made so because several useful properties now apply -- mostly, given a randomized starting alpha value, you can now fade particles out.
Made generation_rate_millis settable too, as generation_rate, while perfectly acceptable, is not actually the name of the property. This violates the principle of least surprise, because I was very surprised to have to access a different key than the one I set.
Added a firefly generator. Couldn't get the curvy motion quite right, or the zordering, but they're fireflies! :D