v0.7.1-beta

Fixed

• Removing, picking or reloading a shader pack in a running world no longer crashes the game.
  The 0.7.0 entry below said the crash was reduced and not gone, and this closes what remained,
  which was two more faults of the same family. A reload freed the pack's images a moment before it
  stopped answering for them, so a pass of that very frame could still be handed them; and loading
  a pack that draws the entities or the hand emptied the graphics device's whole pipeline cache at
  an instant where work already recorded still named what was destroyed. Nothing empties that cache
  any more: the game does it itself on every resource reload, which is the one moment it is safe.
  What that leaves is cosmetic and brief: after turning a pack on or off in a world, an entity or
  the hand drawn by the game's own shader can look wrong for the second or two a pack takes to
  finish compiling, and a resource reload clears it. Tried at length on both loaders, turning packs
  off and on and switching between four of them, where one to four such gestures used to end the
  session.