v8_3 -Polish Pass

Happy with how beholdin' is starting to look, and I've unified the visual design work to a couple of shaders instead of the tens I was using before.  It just took some time to hone in on the methods I wanted to use.  Although I think the visuals have improved a ton recently (AA and thoughtful palettes, mostly), I'm dedicating 8_3, primarily, to polish.  The roadmap for this milestone is below.  I copy and pasted it straight from my planning and design doc, so some of it may not make sense.

-v8_3

        blast blocks? - seems good
        new snake head for reflect snakes i think
        need enemy HIT particles / animation
        Fix screenShake for player (try noise on cam,and the other thing)
        Better hit animation for player - mirrored in UI
        need enemy DEATH particles/animation / slime?
        better looking baddie bullets
        better looking turrets
        better looking homing missiles
        take some time investigating snake bug, hopefully consistent repro