@onlyworlds/sdk 4.15.0

Added

• changesHead(): GET /changes?head=true, the feed's position now without a page
  (keel reads no element). Returns { head, cursor }: head is the world's change_seq,
  cursor a position to pass as since that re-sends nothing (a guest's carries its view's
  epoch). The cheap "anything new?" for a poll: compare head with the head you last applied
  and walk changesAll only when it moved. keel sends the owner's cursor as a number; it comes
  back as a string, like every cursor the SDK hands out. Checked live on Moppetopia: a walk
  from the returned cursor brings nothing. Asked for by Lantern's 20-second poll (Temper,
  Skeld's S15).