Pebble

Bug fixes from #15 and #16. Thanks to @Towboy22 and the #16 reporter.

Fixed

• Doors and beds now render as coherent two-block objects. Each half samples
  the correct portion of its composite texture, beds drop only one item, and
  using, exploding, or naturally destroying a bed consistently addresses both
  halves.
• Levers now look and move like mounted controls. Their base and handle
  follow the face they are attached to, use focused texture regions, and visibly
  change pose when switched.
• Slime and honey blocks now move their attached payloads with pistons.
  Sticky-piston retraction preserves the full adhesion set, and retracted piston
  bases can move so basic flying machines work.
• Equipped elytra are visible in third person. A textured wing layer now
  follows the player and changes pose during elytra flight.
• Running no longer makes the third-person camera weave. View bobbing is
  restricted to first person and its remaining motion is substantially milder.