Kino 0.2.0

• Strip debug info from release builds.
• A panic in the native layer now raises a RuntimeError on the affected
  worker (visible to on_error and the error log) instead of killing the
  server process.
• The pidfile is claimed exclusively: starting refuses (instead of silently
  overwriting) while the pidfile's owner is alive, a leftover file from a
  dead process is replaced, symlinks are never followed, and shutdown
  removes the file only while it still holds our pid.
• Zero-copy response bodies: bodies of 4 KB and up ride to the network
  layer by reference instead of being copied at the FFI boundary, in both
  dispatch modes. A 10 KB-body endpoint now serves at plaintext speed.