Added 3-1

The recent PixelRender fix was targeted to the pipes here
Fix for Pirhanas

The name needed to be changed, and the bottom of the Piranhas needed to
be set on height changing.
Fix for Piranhas staying upright

If the Piranha stays upright for > 4 hours, please see a physician.
Added 3-2
Added 3-3
Added 3-4
Added 4-1
Fix player crouching height

It looks like the player is still showing the running sprite while
crouching. Hmm.
Added 4-2, slightly changed maintainSolids

maintainSolids should work a bit better for removing old solids. Also,
all .json files now have the piranha name change too.