creepers should drop sand on death and the destroyed player-placed blocks

Creepers should drop either gunpowder (chance of 55.6%) or sand / red sand (chance of 44.4%) on death, which would finally make sand a renewable resource. This would also mirror the crafting recipe for TNT.

All player-placed blocks should be dropped if they are blown up by a creeper, making fixing the left-behind damage less tedious.