Add simple transparent cloud block
Added quad geometry shader and made correct render order for transparent blocks
Minor simulation fix
All blocks affected by gravity.
Rename dirty -> remesh
Remove BlockRef from model_simulate_gravity
Cleanup
Misc fixes

Cleaner exit: join stall alarm thread and force exit with  _exit()
Rename: Block::water15 -> Block::water
Remove partial water blocks from palette
Enable softer ambient shadows for transparent blocks (water / clouds / glass)
Started working on cylinder collision model
Player movement and jumping with inertia (collisions don't zero velocity)
No falling when underwater.
Fixed cloud blending regression.